Intimately coupled with the whole complex of environmentalism and sustainability is the Amazon rainforest. No other area of earth has been as much in the news and in our consciousness in the past few years. In terms of biological diversity, natural resource potential and ecological influence, this area of the world is one of the most significant. This is not to demean or belittle any other area, far from it. Rather, the highlighting of the Amazons in both its actual and symbolic significance for life on earth is to contribute to the greater understanding of the need to preserve all habitats, human and non-human. The awareness of the interconnectivity of all life and the consequences of this view serve to accentuate the need for rethinking our relationship between our own activities and the world around us.
Over the past twenty years, the fight has been on to save the Amazon and to protect its Indian lands. Pertinent in this struggle is the construction of the last sector of the BR-364 Road which would give the general population, as well as the timber industry, increased access to the Amazon and its wild resources.
Some of the greatest environmental and geological studies of the Amazon Basin to date have not been made from the ground but through the use of remote-sensing technology. Many specialists have long recognized the need for classifications of the vast biographical domain of the greater Amazon Basin. Deforestation is clearly contributing to the build-up of CO2 in the atmosphere, yet the actual amount of deforestation for a long time was largely unknown. It was found that no one system of remote sensing could provide the answers. Therefore both spaceborne and airborne radar images were acquired of portions of the Middle and Upper Amazon Basin in the State of Amazonas and the Territory of Roraima. The radar image data sets were obtained not only by Shuttle Imaging Radar B (SIR-B) in 1984, but by SIR-A in 1981 and by Radambrasil which operated from 1970 to 1985. The radar device used was able to penetrate clouds and the jungle canopy to reveal the surface features below. Radar has proved to be an effective supplement to Landsat and NOAA observations because of persistent cloudiness in the tropics. Remote-sensing radar can reveal features such as agricultural fields, urban areas, mountain ranges, and water surfaces.
Radambrasil mappings were compiled into 38 volumes of between 300 and 500 pages each. Radambrasil used a research airplane to take radar photos that covered a circular area of 37 kilometers in diameter. An altimeter registered the changes in altitude, but the plane attempted to maintain itself at 11 kilometers above the ground. For SIR-A and SIR-B data which was acquired from NASA’s Shuttle flights, wavelengths from the radar system on board was set to 23.5 cm. SIR-A had a standard 50-kilometer swath width. SIR-B swath varied (20-50 kilometers) depending on the orientation of the antenna and with the bit rate and the variable antenna depression angle. The Amazon Basin is so massive that it would require approximately 400 Landsat scenes unless a sampling strategy was adopted.
In comparison, Radambrasil used a depression angle of 7-25 degrees as opposed to the 37-43 degrees depression angle used on SIR-A. A depression angle is the angle from the airplane, measured horizontally down to the surface, whereas incidence angle is the angle from the ground up which is complementary. Radar pulses that strike a horizontal surface at large depression/small incidence angles produce strong return echoes, while pulses that strike the same surface at smaller depression/larger incidence angles produce weaker radar returns. Differences thus are analyzed between the angle of the radar system and variations in surface relief and roughness.
The rate at which the backscatter decreases with increasing incidence angle is governed primarily by the physical characteristics of roughness, slope, dielectric constant, and moisture on the surface. As a general rule, a rougher surface will produce a stronger radar return than a smoother surface at incidence angles greater than 30 degrees. In some cases, the Radambrasil image showed clearer drain angle patterns because at relatively large incidence/small depression angles a greater shadowing effect occurs . This clarity is also effected by the closer proximity of the radar.
However, the lower depression angle sometimes failed to penetrate the jungle canopy. In the area of the Rio Negro, the flood-plain is also clearly distinguished and outlined showing contrast in image tone by the Shuttle radar, but not visible except for some relief information on Radam (Projecto Radar da Amazona) images due to the low depression angle. There is also no contrast along the length of the drainage to indicate flooded conditions on the Radam image, but appears on SIR-A as a cut-back condition. Similarly, the alluvial forest by the rivers Santa Helena and Taxidermista is completely indistinguishable by Radam and there is little or no contrast with vegetation from each side of the floodplain. At the much larger depression angle used on the SIR-A, the alluvial forest appears very bright in marked contrast to the forest on each side of the floodplain.
Taking into consideration variables such as time of day, incidence angle, etc. it is theorized that in particular regions of vegetated areas (excluding swampy areas) SIR-A brightness tends to increase with the vegetation index. Uncut areas are textually rough and, therefore, had a moderately strong radar return. Recently cleared regions showed increased spectral reflection, but older cut areas used for pasture land or vegetation were less bright due to the dielectric effect in wet regions, or because abandoned, previously cleared areas often have a rougher texture than even the primary forests, and are less efficient volume scatters, showing a stronger return signal.
SIR-B has multiple angle imaging capabilities and therefore can collect pictures using a greater range of depression angles (from 30-75 degrees) so they can be used to differentiate surface materials on the basis of their roughness characteristics in much the same way that Landsat imagery collects information in multiple spectral channels to identify materials on the basis of the way they reflect sunlight.
SIR-B data experienced technical problems while flying over the area, but it showed forest clearing near Alta Floresta and Sinop in northern Matto Grosso. Near Sinop, some 200 farming plots were evident. They are generally long, in lattice-like patterns, and in narrow clearings parallel to one another. Most plots are smaller than 200 hectares indicating small operations of family farmers. In contrast, there are several clearings of 6000 hectares. Clearings of such a large scale usually are for commercial cattle grazing. It is becoming more essential that information on vegetation structure and regrowth be available to help separate primary forest from secondary regrowth.
Thus, scientists have been able to witness through remote-sensing, which produces both two and three -dimensional pictures, the first-hand destruction of massive hectares of forests robbing nature of the last ecosystems for the survival of the Indian people. There is no doubt that large-scale environmental changes are being created by population influx and land development. Computer simulations based on extensive historical data suggest the Amazon’s rainfall can be expected to decline radically as drainage and deforestation proceed; then as deforestation proceeds, reforestation becomes nearly impossible.
Brasil’s former Minister of the Environment, Dr. Jose Lutzenberger, was the visionary who saw the role of interdependence between the Amazon and the world. His plan was for education, research and protection policies to create a realistic authority over environmental units in each of Brasil’s twelve government ministries to form a “consensus strategy” for long-range preservation of both land and wildlife, but before long he was displaced from his position.
Reacting to worldwide concern over the devastation of the rainforest, many claim there is no need to worry . After all, burning forests in Amazonia only account for less than 20% of the total increase in atmospheric carbon dioxide (according to Prof. A. Goldemberg, University of Sao Paulo, Brasil). However, the burning of the rainforest is doing more than just increasing carbon dioxide. The Amazon is the “great heat factory of the world”with a daily energy turnover equal to some six million atomic bombs. One of the great ironies of the modern industrial society with its remote-sensing technologies is that we can now see planet Earth as a whole as a living biosphere. Yet, down here, we continue to behave as if we were blind.
Looking at the Amazonia from a satellite perspective, we see that the air masses, as shown by cloud movements, travel into central South America from the Atlantic, go west and hit the mountain chains of the Andes. There the flow splits into several branches. The central part rises over the mountains into the Pacific and continues west along the Equator, roughly following the convergence of the warm northern sea current, El Nino, with the cold Humboldt stream that comes from the South. These are systems of interconnected ocean streams and air streams which are responsible for the incredible richness of life in and above the waters of the west coast of South America and where in the last two decades we have seen the serious “flip-overs” of weather that have caused overnight collapse of the fishing industry.
However, according to Lutzenberger, the air currents over the Amazon do not only affect South America. The currents connected with El Nino effect the weather pattern over Central and Southern Africa. Moreover, the air masses over the Amazon work like a giant vortex and spawn off air currents that are capable of traveling as far north as the eastern coast of North America which in turn merge with the Gulf Stream air which reaches and penetrates Northern and Central Europe and may be the cause of the “green vegetation” in northern Norway.
What will happen if the Brasilian rainforest disappears? The forest makes its own climate and is the result of that unique climate. What if devastation continues at the present rate? Most everything could be gone by the year 2025 AD. A hundred thousand square kilometers of primeval forest are cleared every year the results of destruction grow exponentially. Land the size of Portugal is slashed and burned every year. And the end will inevitably be: (1) a change in weather, (2) an increase of drought and desert, and (3) massive starvation for many peoples, regardless of background and world economics. With large land parcels being given away for exploitation, there is absolutely no way, even with Radam surveys, to oversee clearance. At the present time, 100 tons of topsoil are lost per hectare each year. The forests that are destroyed will take a thousand years to regenerate. With their destruction goes the refugia of a species diversity entirely preserved from the early periods of evolution the Pleistocene era in our “present” time: with color morphs, strange and beautiful speciations, butterfly wings of color.
All of this is being steadily destroyed, and there is human tragedy as well. At least 87 Indian tribes have become extinct this century. Anthropologists have seen an overall Amazonian aborigine population decrease over the past 500 years from an estimated 6.8 million to the present 125,000. Anthropologist Emilio Moran cites disturbing research indicating the decline of the Parakana and Nambiquara indigenous groups within very short periods of time due to the influences of outside companies, ranchers, and road workers whom the Indians call the “termite people.”
As highways and small farmers who are simply trying to create a livelihood intensify their own slash-and -burn techniques throughout the Amazon basin and more and more ruropoli (frontier family villages) of some 48-1000 people spring up in various locations throughout the Amazon the forests are razed, the inroads flooded, the Malaria vector is strengthened, intense soil erosion occurs, and the river fish species die out. The tragedy is that most of these small family plots created by hundreds of thousands of new inhabitants are only able to sustain crops for a limited number of years because of the rainforest terrain. Therefore, these farmers must move on and find new land to utilize. So what happens to their old plots of land? They become wastelands with small brush, because the original trees cannot grow back due to their root structures and because the soil has been destroyed and removed.
In the wake of vast devastation throughout the Amazon, only now has the revelation of global atmospherics impressed biologists. The Amazon is the critical link in the Earth’s carbon dioxide clearing house. Furthermore, Amazonian Indians and forest species possess the richest repository of native wisdom and potential medical, and technological plant products of any other region of the planet. But the metaphor of human disruption since the sixteenth century is fully at work in Brasil. The country is the vortex of ecological imperialism and new deforestation. A generation of embattled conscience has arisen in Central and South American writers who have responded to the political and moral crises with an anguished outpouring due to the mismanagement of such critical factors as: population growth, political agendas, and regional economics. Nobel Prize winner Garcia Marquez (The Autumn of the Patriarch) and Vargas Llosa (The War of the End of the World) are but a few of the many testimonies of this anguish.
Our time has now come to work for new cooperation in this and other critical environmental regions. Our species is the only one to lay claims to being able to influence the make up of the natural world. We long ago drew up the battle lines. Today, that struggle is most dangerously pronounced in the tropics, where soil is in short supply and human food is at a premium. The Amazon contains some 550 million hectares of rain forest, 3.5 million square kilometers, nearly half of the Earth’s water moisture, easily a million plant and animal species. In but 2 hectares of Amazon forest, 173 floral species have been discovered on a base of 900 metric tons of living biomass. In short, for several thousand years, life has been fashioned according to its evolutionary laws and in the Amazon basin archaeological relics suggest an early habitation at the mouth of the Amazon dating back as far as 5000 years. As a part of Eden on earth, its destruction may also signify the end of life as we know it. It is our time to make the change to work together to expand the lifetime of the Amazon Basin in Brasil so that there would be no end of real civilization, but a wise and practical preparation for the opening of the high frontier in meeting with other cultures and cosmic civilization in the 21st century.
Laser Remote Sensing of Forest and Crops in Genetic-Rich Tropical Areas
Dr. Edgardo Gerck
Campinas, SP, Brasil
Dr. James J. Hurtak
Los Gatos, California USA
[Originally published in International Archives of Photogrammetry and Remote Sensing, Vol. XXIX, 1992, ISPRS, Washington, D.C.]
The benefits of using laser remote sensing are discussed in the context of inspecting large and inaccessible South American areas of forest and crops. Laser remote sensing advances traditional radar technology with benefits of shorter wavelengths, less beam divergence and wavelength selectivity. In the South American areas of interest, species that need to be monitored are either only locally available or show important local genetic or soil influences. The application of LIF lidar techniques for forest and crop monitoring thus has to be developed in close contact with the large genetic variety found, for example, in the Amazon Region.
KEY WORDS: LIF lidar, SAR, chlorophyll a
Optical remote sensing from airborne operations can be either active, by inducing a distinctive response through a broad-band or selective stimulus, or passive, by purely spatial and spectral analysis of reflected light.
Active monitoring of environmental changes, terrain profile, water abundance, gas temperature and concentration for various molecules, clouds and other parameters of special relevance to forest studies, have been carried out using various laser techniques. Purely passive spatial and multispectral analysis of LANDSAT and SPOT data have also provided valuable tools for remote sensing of forest areas. (Hurtak, 1986)
Helped by field studies, both techniques can be used to classify land use mainly as forest, cleared areas, pasture, and secondary growth vegetation. These four main classes are, however, highly variable and transitional into each other. For example, pasture can be only grass or a mixture of grass, crops, soil, and slash. This further complexity lowers the analysis confidence factor and even prohibits a finer analysis, such as crop type determination or species monitoring.
However, there is a need for more information than current land usage analysis can provide. Crop estimates, spread of plant disease, control of illegal crops, selective deforestation, crop species abundance profile, and other detailed vegetation data, are highly needed on a reliable, short-time basis. In the Amazon region, collecting the detailed vegetation data can be even more challenging because of the genetic variety observed even in same plant species. Furthermore, the inaccessibility and vastness of the majority of the Amazon region forest and farm areas make it mandatory to use remote sensing methods, because field analysis would not be feasible.
This paper deals with measurement techniques and issues pertinent to the remote sensing of finer vegetation data, by using laser induced fluorescence (LIF), both differential and excitation-selective.
2. PLANT LUMINESCENCE
Lasers, by inducing fluorescence in plants, can be used to monitor plant species, through its signatures in multiple wavelengths. Yentsch and Menzel (1963) showed that a fluorescence technique could be used to determine the concentration of chlorophyll awith phytoplankton. The fluorescence time is short, close to a nanosecond. Many plants demonstrate high spectral absorption in the 430nm -575nm within the violet and blue visible spectrum. Chlorophyll amolecule P680 is detected between 650 -685nm and its return fluorescence can be used to measure the efficiency of photosynthesis.
Plants also fluoresce in the presence of UV wavelengths (300-380nm) from pigments other than chlorophyll a. Bands from 530nm-575nm can be used to locate paved surfaces and minerals such as iron in rocks and soil. Bands of 770nm-810nm show cellular arrangement and water content.
Chlorophyll agenerally shows little variation over different types of leaf, although chlorophyll combines with different proteins to form chloroplasts where one leaf cell can contain 50 chloroplasts. Four kinds of chlorophyll exist (a-d ), with chlorophyll babsorption peak in the 480nm region. Leaf pigments of carotenoid, and anthocyanin are relevant in determining plant types. The presence of carotenoids appears at 460-500nm. Absorption by anthocyanin is within similar wavelengths of 400-550nm, both far shorter than the P680 chlorophyll peak.
Visible pulses from argon or dye lasers with powers in milliwatts are known to excite chlorophyll and phycoerythrin (a red pigment phycobilin). The difficulty has been in determining calculations for reflectance applicable to a majority of plants due to their complex multi-layered structure (i.e. , monocotyledonous, dicotyledonous) containing both scattering and absorbing materials. Willstatter and Stoll (1918) explained plant reflectance based on light at the cell-wall-air interface of mesophyll tissue. Another approach tested is to treat the leaf as a scattering and absorbing turbid medium (Yamada, 1991) using the KMT theory (Kubelka-Munk theory) of modeling light in a multilayered object.
A dicot leaf can be composed of as many as six layers, i.e., two waxy external cuticular layers, an upper and lower epidermal layers, a mesophyll layer, and a palisade tissue layer. The cuticle layers are composed of cutin and contain no pigment; hence no absorption, whereby the sum of reflectance and transmittance of the layer is equal to unity. The palisade tissue layer containing pigments and chlorophyll is densely packed allowing negligible scattering. The mesophyll layer contains the absorbing and scattering materials such as chlorophyll, other pigments, and cells that are uniformly distributed in them, according to their unique optical properties. Calculations are best gained from analysis of both the palisade and mesophyll layers.
Florescence Studies for Corn Crops (Monocot)
The monocots can be differentiated from dicots by virtue of having a higher fluorescence intensity at 440nm than the fluorescence intensity 675nm-740nm from the chlorophyll amolecule P680. Present evident indicates that the fluorescence in the 675nm-740nm range may also determine different plant types by the working of two different photosystems. In one photosystem, the chlorophyll amolecule P680 peaks as previously described. In the second photosystem, the chlorophyll amolecule P700 peaks which may not be a unique molecule but a dimer of two chlorophyll amolecules in association with special proteins in the membrane. Both systems can occur within a plant simultaneously.
Analysis can be made thus by measuring reflectance and transmittance integrated over a hemisphere at each wavelength. For the chlorophyll amolecule P680 wavelength from 0(875nm) to x (650nm) can be used. A minimum of three bands of close proximity best determines the scattering coefficient and the slope of the peak. This peak range eliminates the contribution from other kinds of scattering and absorbing materials within the leaf so one can calculate the chlorophyll content per unit area.
The results are aimed at confirming the spectral absorption coefficient of chlorophyll pigment with maximum peaks at 440 and 680nm, as well as the absorption coefficient of other pigments contained in a leaf.
According to Yamada, by selecting wavelengths with large absorption coefficients, one loses accuracy at large chlorophyll contents and gets accuracy at small chlorophyll contents. By using wavelengths with small absorption coefficients, one can achieve relatively lower accuracy over the whole range. Wide bandwidths usually reduce errors in the reflectance and transmittance measurements. However, they also reduce the linearity between absorption coefficient and pigment content, especially when measuring the slope of the peak. (Yamada, 1991)
Candidate lasers are the solid-state lasers such as the Nd:YAG (532nm-3µm) pulsed from 100 – 200 Hz proven
effective for measuring chlorophyll a. Other possible laser wavelengths have been used, but for spaceborne lidar Nd:YAG currently offers the most developed technology. The 355nm is sufficiently short to be dominated by Rayleigh scattering. The 1064 nm wavelength is sufficiently long to be dominated by aerosol particle scattering in the lower troposphere, with poor noise properties from available APD detectors. The 532nm wavelength is suitable for both aerosol and molecular scattering having good detector characteristics.
Both flashlamp-excited or diode-array excited Nd lasers can be used, to provide the necessary S/N ratio. The lasers and accompanying equipment can be assembled as mobile land units or airborne devices. In the case of choice, as airborne devices whenever possible, the equipment can be flown by helicopter or plane and must be light-weight and sturdy.
In addition solid-state lasers, the TEA CO2 laser at up to 11µm can be operated at PRFs of up to 300-400Hz with pulse energies of a few hundred mJ.
4. LIDAR FOR AIRBORNE REMOTE SENSING
Monitoring of crops and environmental changes can be performed from airborne operations to provide large scale surveillance uses topographic lidar based on high S/N ratio. In studying soil or topography, each laser pulse can be used for a unique range measurement and waveform data.
Essential in airborne monitoring interpretation is aircraft pointing attitude data for range measurements, recovery of accurate surface elevation, and assignment of the elevation data to the correct Earth surface location. Laser altimeter signal strength depends on laser pulse power backscatter from the target surface and collected by the receiver telescope. Competing processes are optical background noise and detector noise. (Bufton, 1991)
For detecting soil, plant, and man-made surface features, the surface backscatter coefficient Rvaries due to the surface type, but can be approximated by Rground= / , (Reagan, 1991) where is the surface hemisphere or albedo with an albedo percentage value of 4-5% for wet soils and 30-40% for concrete structures. Trees and crops have a 15% albedo value for 532nm and 60% for 1064nm wavelengths. Using two or three beam pulses, the beams can be transmitted simultaneously and then detected in order to derive backscatter profiles at these wavelengths.
5. DIFFERENTIAL-SAR DETECTION TECHNIQUE
During one measuring event, the plant species is selectively excited by a narrow-band laser emission and fluoresces. The intensity dependent fluorescence band and the fluorescence decay time must be measured.
Because of the relative movement between source and target and because of the non-specular nature of the fluorescence, if the fluorescence radiation is collected by a line detector then the total yield is very low.
Also, if the detection method does not compensate for wind, moisture, background fluorescence from unwanted species, angle of absorption, etc., then the measurement is masked by important calibration factors that are time-varying and weather dependent.
The LIF method being reported in this paper, proposes to solve both problems by a combination of Synthetic-Aperture Radar (SAR) signal processing with differential fluorescence measurement.
Analogous to SAR, the receptor is a bi-dimensional array of point detectors, connected (in parallel in each row and with a computer controlled delay for each row) to a series of summing units that coherently adds the light intensity collected in each point to a point further in time. The coherence is maintained between source-target velocity and summing point, achieving a synchronism between the time scan of the array and the areas scan of the target. This technique is also similar to the Time Delay and Integration (TDI), nowadays a common signal processing technique for CCD detectors [EGG&G, Sierra Scientific, and DALSA are the main manufacturers] in low-light level moving inspection systems. The analogy to SAR is the effective increase of the detector (antenna) area, by signal processing. Since the intensity addition is performed immediately upon detection, the S/N ratio is not largely influenced by the further processing stages.
After the SAR-type detection (with on-line signal processing), the signals are available in various bands as a function of the target scanlength for each fly-by coordinate. These bands are chosen to provide for a variety of differential combinations that can uniquely identify a particular species by its fluorescence spectra. With the time analysis of the differential combinations (based on the fluorescence lifetimes for each chosen bands of the particular species), a further discrimination factor is added as a time-correlation for each differential signal, in pairs. The time-correlation data reduces to a function of the target scanlength, which is the confidence level in 0% to 100% of finding the particular species in the target. The spatial resolution is a trade-off between sensitivity and background noise and can be adjusted by adding together one or more detector lines in each row.
The experiments under way to apply the above technique to an actual case have three main steps: (1) Modeling the method and calculating the actual laser/detector/electronics parameter; (2) Measuring the various differential spectra in the laboratory for typical plants of interest; and (3) Setting-up a first system for mobile or aerial use. The first step is being completed together with some sample measurements.
This paper has presented a high-sensitivity method for detecting plant species in genetic-rich areas, with a LIF technique. The method is based on increasing the S/N ratio immediately upon reception by coherent addition of the multispectral fluorescence intensities, band for band, and by performing a ladder of cross-correlations of the time-dependent band signals, that takes into account the dynamics of the decay channels. The resulting signal is a function of the scanlength covered by the plane after the starting coordinate, and represents a series of confidence levels of finding the species along the flown line.
The application of this technique can lead to better law-enforcement control of present issues such as illegal crop production and unlawful deforestation, as well as an improvement in agricultural planning and crop estimation.
Bufton, Jack L. et al. 1991. “Airborne lidar for profiling of surface topography.“ Optical Engineering 30(1):72-77.
Ford, John et al. 1986. Satellite Radars for Gelogical Mapping in Tropical Regions. Presented at the 5th Thematic Conference: “Remote Sensing for Exploration Geology,” Reno, Nevada.
Hurtak, James, 1986. Airborne and Spaceborne Radar Images for Geology and Environmental Mapping in the Amazon Rainforest, Brasil. Symposia Latino Americano De Sensoriamento Remoto, Vol. 1. Gramado, Rio Grande do Sul, Brasil.
Reagan, John A. et al. 1991. “Spaceborne lidar remote sensing techniques aided by surface returns.” Optical Engineering 30(1): 96-101.
5. Yamada, Norihide et al. 1991. “Nondestructive measurement of chlorophyll pigment content in plant leaves from three-color reflectance and transmittance.“ Applied Optics 30(27): 3964-3973.
The shuttle imaging radar (SIR-A) carried on the Space Shuttle Columbia (November 1981) penetrated the dry Selima Sand Sheet, subsurface valleys and arid desert wastelands of the eastern Sahara, revealing previously unknown buried valleys and channels, unusual geologic structures, and possible Stone Age occupation sites, not detectable by Landsat. The calculated depth of radar penetration of dry sand and granules, based on laboratory measurements of the electrical properties of samples from the area extends, in some instances, to a depth of 6 meters. Field studies in Egypt verified SIR-A signal penetration depths of at least 1 meter in the Selima Sand Sheet and in drift sand and several meters in sand dunes. Subsurface findings at various locations from Kom Ombo to the Chad-Sudanese border suggests a massive paleo-drainage system that flowed in an west-east direction.
RADAR MAPPINGand Paleo-drainage in N. Africa:
The presence of old drainage networks beneath the Selima Sand Sheet, dunes, and drift sand of the eastern Sahara provides a geologic explanation for the locations of many obscured playas and present day oases. This discovery originally made by SIR-A has revealed one of the major centers of episodic human habitation based upon a vast, now-vanished paIeo-drainage system. The existence of this drainage system is of paramount importance to the original continental framework of Northern Africa. The area of concern is the Arabian Desert that exists in the eastern Sahara. There are a few traces of gravel that were detected on the ground by Landsat, but prior to the SIR-A survey, no one had any appreciation of the true typology beneath the Sand Sheet and the dunes presently dominating this region.
The present Nile system runs along Egypt with its tributaries of the blue Nile and the white Nile, then over the crystalline rocks of the Red Sea Hills, the upper Arabian shield which is a zone of sea-floor spreading. (1) This spreading began in the late Neocene — about 40 million years ago. In terms of the overall geomorphological picture this is a very important element, since it would indicate that this is a relatively active area. In addition near the border of the present Nile system there are various volcanic centers such as the Amhara Triangle in Ethiopia and the Tibesti Mountains in Chad. These are late Tertiary volcanic constructs which began with doming, followed by volcanism, sedimentation and the like.
1.1 Evidence in East Africa
In the midst of wind-eroded standstones in Chad, signatures of an ancient drainage system have been identified through SIR-B. Just south of the Libyan Desert area and east of the Tibesti Mountains, the bedrock formations of Devonian sandstone show varying resistance to erosion. Different image textures seen on SIR-B imagery of Northern Chad, indicate the presence of four sandstone units whose boundaries are marked by bedding scarps. Pronounced drainage channels can be seen between sandstone of very low relief, sand veneer and limited areas of outcrop. It is an area of flat terrain with a thin veneer of dry sand parallel to the dominant wind direction. The strike of the sandstone units is in the range direction. Gullies appear as extensive dark linear streaks that are nearly normal to the strike of the bedrock units and are in response to a lengthy period of wind erosion. (2) All these formations added to the greater picture of the ancient drainage channels have lead investigators to theorize the existence of a former wetter climate in this extremely arid region.
First seen by remote sensing, in the eastern Sahara there exists a large, very well expressed alluvial valley. In 1984, Ron Blom and colleagues carried on extensive fieldwork at the location of one of the Wadis (streambeds) in south central Egypt close to the Sudanese border. The purpose of their research was to verify and explain the topological findings from the SIR-A. Initial observations suggested a previous role of fluvial activity quite different from the present aeolian landscape.
One of the main research criteria was to demonstrate why the basin and valleys showed on radar such a great contrast from the surrounding terrain? Their research revealed great alluvial valleys that at one time carried large amounts of water, braided stream complexes and carved bedrock control channels. What Ron Blom and colleagues encountered, came to be called “radar river” systems. And on the south shore of one of the valleys out of this fluvial environment came a collection of early stone‑age artifacts, suggesting that Homo Erectus (early man) produced hand-axes about 250,000 years ago.
New vistas were gained into the character and significance of these valleys from diggings which showed there were massive areas of caliche sedimentary rock that was capable of being formed into nodules. This rock was extremely dense and covered by a very thin layer of sand sheet that is essentially transparent to the radar signal. The upper surface of this is quite rough at about the 10 cm scale. The sedimentary rock turned out to be the key to the braided stream channel complex. (3)
In some cases the signatures on the radar images show structural depressions and probable buried intrusives, as well as infiltration of bedrock crevices by windblown sand and collovium. This results in a dark response to SIR-A and has enhanced the patterns of these structures on radar images. In the soft area in the northeast corner of Sudan-Egypt a very complicated braided stream complex was discovered that gives rise to two important questions. Why do the islands appear as intermediate albedo on radar? And why do the channels which are there appear very dark? Extensive diggings were made within the channels via a series of trenches (set at five meter intervals) which revealed an inset channel system that also existed within the caliche (calcium carbonate). It was determined that the SIR-A radar was penetrating the uppermost sand layer, but scattering back part of the signal from these volume scatterers at a shallow depth. In effect, the dark response on the radar was going off somewhere else after reflecting off the interface and the signal and was not being recorded on the spacecraft.
The Sand Sheet is not a sand dune, but is a planar ubiquitous type of unit, the likes of which are not found anywhere in North America, nor in most of the deserts of the world. It is almost unique to this part of the Sahara and is organized into well-developed bed‑forms that have amplitudes no greater than a meter, such that when one scans the surface one cannot discern this relief. The wavelengths of this are 1/2 to 1 kilometer; they are extremely subtle forms with no slip faces. In addition to trying to establish the sedimentary environment, Blom and others had to work very hard to explain the radar physics and especially the caliche nodules along the walls of trenches in the crystal sand which is a massive fluvial unit. These nodules turned out to be of the right size and the right distribution to give an intermediate (radar) response after having the radar signal pass through the very thin upper unit of the aeolian sand sheet.
Direct on-site investigations further demonstrated the reality of these fluvial sediments, showing that they are not simply an anomaly of the radar imaging system. A large series of trenches, 2 to 3 meters deep and 10 meters wide were constructed. (4) In the walls of these trenches, sand sheet was found on top with other loose material — and beneath petrogenesized older sand sheet (brick-like in character), was an aeolian nonconformity covering an alluvial sequence. There was found all the earmarks of deposition in a fluvial environment. For instance, in the deposits were gathered examples of fresh‑watered mollusks, one of which is a biofulariaflyferide which is a species that can live only in stony fresh-water environments, along the banks of fresh‑water streams supporting vegetation.
Researchers at the site have brought up to the surface several hundred meters of geological strata from below. They also incorporated in their findings the seismic work done by German engineers that showed a large difference in velocities (between 350 to 800 feet per second in the upper unconsolidated and 1100 to 1500 feet in the consolidated below). The bedrock stretches from 4500 to 5600 seismic velocities — thereby showing density effects velocity providing the bedrock is of different density.
The geological samples gave remarkable cross-sectional evidence of a fill area changing somewhere between the Tertiary and Pleistocene epoch when aridity began to set into the Sahara about 2 million years ago. The streams changed from earlier cycles of humid environmental characteristics, from tropical conditions in the Neocene and the Oligocene to the later Miocene and eventually to the semi-arid conditions beginning probably in the Pliocene end of the Tertiary period.
Fluvial activity may have continued into the Quaternary period which is known to have a number of fluvial periods, theorized by some to have taken place: 8,000, 50,000, and a major fluvial period 300,000 years ago. Each fluvial activity appears to correspond to a major period of human occupation in the area.
Evidences gathered from regional considerations, from a series of excavations in the Wadis that were explored and some of the larger alluvial valleys were sufficient to create a model of what one of these “radar rivers” looked like. (5) The major sources used to create the model were from the geophysical information pertaining to the depth of the various strata, the alluvial sequences and information from the velocities of the various strata supplied by the General Petroleum Company (of Egypt) seismic team. Researchers, Ron Blom and colleagues, have deduced that at some early Tertiary period of earth’s history the environment in this region was humid, with massive streams flowing throughout southern Egypt at a period even before the course of the Nile River as we know it today.
1.2 Radar Implications in Egypt
We have a model for early fluvial activity in the region of northern Africa, but we are still faced with a major question of where did these rivers come from? The exciting implications are as follows: The mid-Tertiary period data along with the SIR-A and SIR-B data put together with all the known drainage lines in this area seems to indicate that the drainage was generally from East to West, during the Tertiary Period. Various confluent rivers and streams are suspected of flowing off what was at that time some of the highest points of North Africa, namely the Red Sea Hills. The flow was across the waistline of Africa toward Lake Chad, before the Tibesti, Darfur and Ethiopian highlands were formed. If these volcanic constructs and rift zones were not there – the rivers, given sufficient drainage from the Red Sea mountains would not have stopped, but may have gone all the way to the Atlantic.
In Figure 1 we see the pattern of the present day drainage in North Africa and the general direction of river patterns as they may have looked in the Tertiary Period The Nile system at the very earliest of its beginnings is thought to have occurred at a time when the Mediterranean dried up – about the late Miocene – 6 million years ago. This would have been the beginning of the Nile, due to an activity which cut a canyon from the vicinity of Cairo all the way back to Aswan with an equivalent depth of the Grand Canyon, but three times as long. The effect of this on the earlier drainage system (early Tertiary period) would be to behead the trans-African streams that were discovered by means of SIR-A radar and formerly unknown. It would have cut off this ancient river system from their head-water. This Nile complex, however, does not appear to have been fully integrated with the head waters until 12-24,000 years ago.
Thus the young and relatively unstable Nile is superimposed as a pirate stream on what appears to be an older drainage system that goes horizontal across North Africa. On the other side of the continent there is the well active Chad drainage (near the Benue complex). Lake Chad was part of a larger system which even today overspills by way of numerous river routes, e.g., into the Benue, a tributary of the Niger River reaching the Niger Delta and the Gulf of Guinea.
The Niger Delta is the largest delta of any river in the world (it is something on the order of 3 to 4 times larger than the Nile delta). This is most unusual. Researchers are now questioning whether the rivers connected with the Niger Delta are vast enough to have given enough water to create this large of a delta. A view of Northern Africa in mid-Tertiary times — some 25-30 million years ago - according to this research would show a much greater trans-African drainage system. This drainage system could easily account for the vastness of the delta system — a river system which spanned from east Africa to Nigeria, later beheaded by the Nile growing southward.
All this information has been brought to light by radar contributions in this area — using both SIR-A and SIR-B — which provided information of the missing links — and stimulated first‑hand field investigations. From the vantage point of radar observation, this river system is still extant even though only the western portion is operational.
FIG. 1 SIR-A showing Paleo-drainage in North Africa
According to Dr. Geoft Lawrence, SIR-B uncovered quaternary sand and gravel deposits over wide areas and long linear dunes in the western desert areas of Egypt extending in a north-south direction. (6) This would imply that the course of the waterflow did begin to change probably as early as the Pleistocene epoch. The scarp of the Gebel area (by the Egyptian-Sudanese western frontier) appears bright in the SIR-B images, whereas large rock pediments in front of the scarps may be partly covered by radar-transparent sand which appears in moderately bright tones on the images. This is in contrast to thicker sand sheets in the interdunal areas which appear in darker tones. It was found that dune surfaces yield radar backscatter only when the radar incidence angle is less than the angle of repose of the dune slopes.
When one looks at the mega-morphology – one sees that the extensiveness of this ancient river drainage system was of the magnitude what we find today in the Amazon. Indisputably today’s greatest river in the world, the Amazon drains a basin that covers 40 per cent of South America and covers an area of over 5.8 million square kilometers. (7) The Amazon’s watershed is drawn partly from the Andes, the width of a continent away.
In fact, Africa and South America separated in the late Tertiary Period when the South Atlantic opened. If one entertains the size of the Niger Delta, the largest delta in the world, the Benue system, the Mandara system, and interfaces these with its counterpart where the vast complex of Amazonian waterways connect with the Atlantic estuary, an enormous parallel of a drainage complex emerges.
It is important to understand the theoretical length and volume of this trans-African system in comparison with the world’s present river systems.
TABLE 1: Comparison of World’s Largest River Systems with the Trans-Africa (Trans-A) Radar River
SIZE OF DRAINAGE
In terms of tectonics, the doming of the Afro-Arabian shield took place creating the trailing edge and the regional slopes of the African continent over a time period on the order of 20 million years — which is four times longer than the oldest recognizable segments of the Nile. The new subsurface findings from SIR-A and SIR-B suggest a complex pattern of swamp, dark lakes, and black threads of waterways connecting paleo-drainages across the waistline of Africa, providing missing links between earlier watershed areas and the enormous delta of Niger. Drilling in this area indicates the present sedimentation formed mainly in the very late Neocene.
In summary, our research indicates that the trans-African drainage system is like a mirror image of the Amazon system and of comparable age to the Amazon. The demise of such a trans-African system in the Pleistocene Epoch can be traced to three causes: 1) the beheading influences on the waterways; 2) the rise of the volcanic areas around central Africa which disrupted the drainage system and, in turn, created a dam complex and a large area of sedimentation on the back side of the volcanoes; and 3) the massive event that finally killed the system was a period of large scale dedication after which the trans-African system was put on a downhill course ever since in leaving Africa drier and drier.
In addition to the region of south central Egypt where the majority of research took place. SIR-B also uncovered various other features in Northern Africa which has lead investigators to a greater understanding of the geological structures in this area. SIR-B over northeast Sudan has been the identification of a major suture line, called the 35 degree east suture, where an island arc assemblage of volcanic and sedimentary rocks was destroyed during the Late Precambrian period. Recent geo-dynamic studies suggest that the 35-degree east suture was an antecedent of faults associated with the fragmentation of the Nubian/Arabian Shield and the opening of the Red Sea. (8) The radar images expressing small‑scale textural differences would suggest that the origin of the Nile complex is to be found in the west rather than the south.
Complimentary Technology for Geo-archaeology
The concept of spaceborne imaging radar was proven by SEASAT, LANDSAT, SIR-A, and SIR-B, extensively utilizing it in the fields of oceanography and geology where the data retrieved proved to be extremely interesting to geologists and energy specialists. This data has been used to discriminate other types of terrain, locating oil shale, limestone and minerals.
SAR does have limitations, yet they don’t coincide with the limitations of conventional prospecting techniques. Consequently, integration of the SAR-technology with proper image enhancement techniques and sonar can greatly improve the accuracy level in any project evaluation.
Spaceborne imaging radar sometimes requires complimentary information in the thermal infrared region of the electromagnetic spectrum. IR laser and spectrometer technologies provide enough information so that potential investigators can decide whether or not advanced cross-track scanning is needed in their research program. Visible, reflected IR, and thermal IR measurements are perturbed to a significant degree by atmospheric effects. Thus the attenuation and scattering characteristics of the atmosphere at the times and locations of the observations must be known as a function of wavelength to remove the atmospheric effects from the signals. (9)
In conclusion, many lessons have been learned over the last ten years about the historical nature of large, complex drainage systems. A well-structured approach is afforded by airborne and space borne radar observations. Through this man/machine interface water conduits, energy recourses, and a complete observation of the entire bio-system in its historical context can be understood.
This system of remote sensing covers a wide range of surface and substructure enhancements. Since the investigation of relevant drainage basins is time-consuming, remote sensing of these systems can give us an integrated understanding of the spatial distribution of vegetation cover, soil type, soil moisture content, ground surface temperature, subsurface water occurrence, and so on over the entire drainage area.
Remote sensing requires a state-of-the-art multiple computer redundancy management concepts, incorporating a multitude of functions to support operations on the ground and in flight. Added to this are considerations and efforts of hundreds of engineers participating in the development, verification, utilization, and support of SIR-A, SIR-B and CV-990 programs in unique energy-related, environmental tasks.
Analysis of co-registration of all SAR images reveals that the radar image data can make a several percentage contribution in rock-type discrimination over LANDSAT and Brasilian RADAM data alone. Incorporation of textural measure from the radar images greatly increases their values and results in an additional 14-percent gain in discrimination ability. Other texture measures found very useful are hue saturation-intensity split spectrum processing, Fourier band-pass filtering, and SPIT processing. The additional dimension of color or the summation of gray values added to the radar image is a potentially powerful image-enhancement tool.
The complexity of the interrelationships and interdependence between various components of drainage hydrology and geomorphology require a multi-systems approach since the subsequent movement of water from the head -waters to its outlet change the structure of the system itself and result in an output from the source not only of water but also of water-borne material in the form of dissolved, suspended, and bed load. In the same way the individual hydrologic processes operating within the drainage basin, e.g., precipitation, interception, evapor -transpiration, soil moisture, and groundwater movement and storage, and the runoff process itself, must be applied on many levels if numerical solutions are to be obtained. Here SAR provides for the synthetic eye for viewing the changing spatial patterns and relationships of terrestrial phenomena viewed as the world of man.
Various geologic applications of radar images may be significantly aided through the use of the methods discussed in this paper such as the SPIT process. It is hoped that these additional methods coupled with SAP and LAS (etc.) will provide great benefits in exploring the energy picture in the 21st Century. It appears that the chief observational contributions will come from seismology, isotopic studies, optical and digital radar systems. Low altitude spacecraft have a strong contribution to make in the global, synoptic measurements of potential fields. In addition, to spatial information, measurements of the global secular variation of the magnetic field is also required.
Most importantly, with this new technology in hand, distance measurements from space shout also contribute to a detection of new energy resources, the monitoring of renewable and nonrenewable sources, and the global cooperation that will be needed in the sharing of high technology for both the energy needs and the ecological balance of the planet. (10)
Consequently, if we ask the right question and if we collect the appropriate data of sufficient accuracy in a timely fashion, these experiments should give us major new insights into many of the energy alternatives needed to address the major problems of the future integrity of our global habitat.
Appendix A: Other Spectral Areas
An overview of the various bands are as follows: P band uses longer wave signals; the frequency is proportional to the reciprocal of the wavelength — so, L-band is 1000 to 1300 megahertz, and this is 3/10 of a meter. X-band is 10,000 megahertz, or 3 centimeters. C band is 5 Gigahertz and turns out to be 15 centimeters. 450 megahertz is below the cellular radio (on earth). Its about 3/4ths of a meter — 70 centimeters. The longer the wavelength, the better chance of getting deeper penetration on the order of (conductivity, etc.) proportional to the wavelength. In fact, snow can be penetrated with the X-band.
Appendix B: Computer Futures with Remote Sensing
Additional information on coupling interface priorities between airborne equipment and processing tools:
1) Coding of some of the necessary algorithms with a fixed point design has proved to be somewhat costly in terms of computer time and memory. Future machines should include hardware floating-point arithmetic with sufficient precision.
2) Spacecraft requirements seem to demand continued increases in on-board autonomy and control system performance, i.e., new computers operating at higher speeds & contain more memory.
3) Use of nonvolatile memory technology, such as core or plated wire, has proved almost essential. It can be power-strobbed and therefore expanded with little increase in power. It is immune to radiation and retains its content when power is removed from the computer, either on purpose or by some anomaly. New space computer designs should, as a minimum, use nonvolatile technology for the program portion of memory.
4) In general, science data processing and micro-control of mission instruments using the central computer should be avoided and proper instrumentation should be brought in. Microprocessors within the instruments can best perform these tasks.
5) An extensive software development and test system that has a high fidelity simulation of the computer’s environment is valuable in uncovering timing and logic problems
Sea-Floor spreading proposed in the early 1960’s by the American geologists Harry Hess and Robert Dietz.
Ford, John P., et al, Shuttle Imagining Radar Views Earth From Challenger: The SIR‑-B Experiment, NASA, 3/15/1986, p. 56.
“Caliche” deposits were found formed by a high evaporation of calcium carbonate water. This material was found as rough, irregularly formed bodies, not consolidated enough to be in the form of Travertine.
Pioneering work is being done by Dr. John McCauley (USGC) & colleagues revisiting/ excavating SIR-A lines in Egypt-Chad, etc. Ground survey work by Dr. Hurtak and associates, 1983.
“Calcrete cementation” structures were found intertwined with radar rivers. Radar rivers were formulated on the basis of subsurface features which appeared as anomalies via SIR-A. Here Calcrete (from “calcium carbonate” and “hard layer”) is identified with Caliche materials, resulting from the binding of sedimentation rock by calcium minerals.
Notes from Dr. Geoft Lawrence, Hunting Geology and Geophysics, Ltd., to Dr. John Ford, JPL., 1986.
Vital statistics in Great Rivers of the World, National Geographic Society, Washington, D.C. 4th Annual Earth Resources Program Review. National Oceanic and Atmospheric Administration Programs and U.S. Naval Research Lab. Programs. Houston, Texas, 1972.
Personal discussions with Dr. Mel Stinson and others and the University of California working on geo-dynamic models of continental drift and Gondwanaland.
ABRAMS, MICHAEL J. and KAHLE, ANNE B. “Recent developments in lithologic mapping using remote sensing data,” Proceedings of the IUGS-UNESCO Program on Geological Applications of Remote Sensing, Seminar on Remote Sensing for Geological Mapping, Orleans, France, February 2‑4, 1984.
NASA’s objectives for the future include: 1) Landsat TM coverage over lard completed & available. Work done on using multi-spectral data to map rock mineral assemblages. 2) SIR-B; SIR-C flown and multi-incidence angle capability utilized to characterize roughness. Some X-band and L-band data acquired simultaneously. 3) Large format camera data analyzed with new image enhancement for selected areas. 4) Progress made on physical basis for utilizing vegetation to map soil-bedrock characteristics and to locate fossil fuels. 5) Some high resolution multi-spectral imaging in reflected & emission part of spectrum, from low Earth-orbit system shuttle.