Until a few years ago, virtually all NASA''s remote sensing was done passively. NASA is now working to develop active remote sensing systems, making use of the very rapid advances occurring in laser and radar technology. To be deployed in the difficult space environment, laser instruments must be rugged enough to withstand vibrations and cold while being able to operate automatically without retuning or realigning the instrument by hand. This paper describes several major NASA research efforts in lidar remote sensing, including hardware and key sensor issues, along with results and expectations.

Results of a study dealing with the conceptual design of a spaceborne atmospheric lidar instrument (ATLID) are presented. ATLID is designed to operate on the Polar Platform, a future earth-observation satellite. ATLID yields data on the height, strength, and depolarization properties of scattering layers (i.e., clouds, planetary boundary layer) in the lower atmosphere.

A space-qualified laser transmitter has been developed for NASA''s Lidar In-Space Technology Experiment (LITE). It is a 10 Hz three color, flashlamp pumped, Q-switched neodymium: YAG system with second and third harmonic generators to produce doubled and tripled wavelengths of the fundamental wavelength of 1064 nm. Space qualification of the laser transmitter was accomplished through a combination of design, tests, analysis and production control processes. The LITE experiment has been manifested for STS 62 (Atlantis) to be flown in 1993. This paper presents the engineering aspect of the space qualification process. A companion paper addresses specific optical issues.

The Lidar In-Space Technology Experiment (LITE) laser transmitter module (LTM) flight laser optical architecture has been space qualified by extensive testing at the system, subsystem, and component level. The projected system output performance has been verified using an optically and electrically similar breadboard version of the laser. Parasitic lasing was closely examined and completely suppressed after design changes were implemented and tested. Oscillator and amplifier-type heads were separately tested to 150 million shots. Critical subassemblies have undergone environmental testing to shuttle qualification levels. A superior three-color anti reflection coating was developed and tested for use on 14 surfaces after the final amplifier.

The spectral characteristics of an alexandrite laser used for making water vapor DIAL measurements are evaluated. The optical servo-system used to lock the laser wavelength on a water vapor absorption line is described. A brief description of the DIAL system is given and the data obtained with this lidar during flight tests in March 1990 are also presented.

Narrowband radiation is produced from a pulsed alexandrite laser when injection seeded with the output of a low-power, tunable, continuous-wave, single-mode diode laser. Injection seeded power oscillators are easier to frequency stabilize than etalong narrowed lasers, are more efficient, and less prone to optical damage. AlGaAs diode lasers are available with wavelengths from 760 to 770 nm in the oxygen A band that can be used for differential absorption lidar remote sensing of atmospheric pressure and temperature. Diodes with room temperature output at 740 nm may be cooled sufficiently to emit in the water vapor absorption band at 720-730 nm for humidity remote sensing. The diodes are driven with approximately 70 mA of current with a 0.5 mA peak to peak sinusoidal dither which imparts a 3 GHz frequency modulation to the output. A photoacoustic cell is utilized to generate a negative feedback signal to keep the diode frequency centered on the atmospheric absorption feature. The diode laser linewidth of 200 MHz is sufficient to seed 2 or 3 longitudinal modes of the multitransverse mode alexandrite laser, giving the pulsed laser a bandwidth of 0.007 to 0.014 cm-

The ability to accurately measure the concentration of gaseous oxygen and its corresponding flow rate is becoming of greater importance. The technique being presented is based on the principal of light attenuation due to the absorption of radiation by the A-band of oxygen which is located in the 759-770 nm wavelength range. With an ability to measure the change in the light transmission to 0.05, a sensitive optical leak detection system which has a rapid time response is possible. In this research program the application of laser diode technology and its ability to be temperature tuned to a selected oxygen absorption spectral peak has allowed oxygen concentrations as low as 16,000 ppm to be detected.

Comparisons of the lidar-derived profiles of the atmospheric structure properties (density and temperature) with the standard meteorological rocket profiles have been made. Seventeen flights of meteorological rockets, using both datasonde and passive falling sphere payloads, provide the first study to compare and evaluate the lidar measurements simultaneously with rocket measurements. The measurements were made at Poker Flat Research Range, Alaska, during the period February through April 1986. The molecular backscatter lidar signal from a Nd:YAG laser has been used in regions of the atmosphere where molecular scattering dominates to determine profiles of the relative atmospheric density. By comparison with radiosonde balloon measurements in the region where the scattering is purely molecular-- typically the 27 to 30 km altitude region--the density profile can be placed on an absolute scale. The temperature profiles have been determined directly from integration of the relative density profile, using the assumption of hydrostatic equilibrium. While the backscatter signals from the region of the atmosphere above 25 km are usually representative of the molecular density, the lidar was developed using a two-color approach to provide added discrimination against particle scatter. By using two wavelengths, 532 and 355 nm, the region where the molecular scattering results are expected to be valid can be discerned. The results show the present capability of the lidar remote sensing technique for measurements of the structure properties of the atmosphere. The results point out the directions for the design of a lidar sounder that can be used as an operational sounder to replace the meteorological rocket and balloon techniques in the future.

It is very difficult for both detectors and data acquisition systems to cope with the enormous signal dynamic range of incoherent lidar systems. The high power of the near-range atmosphere-backscattered radiation may cause serious problems to detectors. If the detector can endure the high power, the dynamic range of the output electric signal still remains a problem. To solve the problems, this paper suggests using a multibeam transmitter instead of a single-beam transmitter. With a multibeam transmitter a significant reduction of the signal dynamic range can always be achieved simultaneously with good near-range coverage even under different atmospheric conditions. Numerical simulations for a differential absorption lidar (DIAL) system measuring ozone in the lower troposphere below 3 km show the advantage of using a three-beam transmitter rather than a single-beam transmitter.

In response to NASA thrusts in Mission to Planet Earth, this paper outlines several technology needs for future space-based lidar/DIAL applications. Several technological ''tall poles'' in flight systems are identified, including the technology for laser transmitters; systems technology; and major electro-optical, structural, mechanical, and thermal subsystems. Technologists must address the key questions associated with deploying these lidar systems in medium-class satellite and aircraft platforms. This involves demonstrating engineering parameters for long duration missions which are affordable in terms of weight, power, and volume. The question of affordability must be tied to simplicity in engineering design and to simplicity in the testing and verification of the instrument performance parameters. This requires sufficient testing and demonstration in laboratory systems to avoid the need for changes in engineering design late in the project life cycle.

Coherent Doppler lidar has been studied for a wide range of velocity sensing applications. While most of the developed coherent lidars use 10 micrometers CO2 laser sources, the newly emerging solid-state lasers at 1-2 micrometers are being actively investigated for use as efficient and long-lived optical sources in remote sensing applications. This paper reviews recent work in the development of 1 and 2 micrometers coherent Doppler lidars for atmospheric sensing.

A novel method for achieving well-behaved far-field laser illumination of remote targets for imaging is described. An assembly based on a mixing rod modifies the laser output to give uniform illumination of a remote target and the laser footprint on target can be closely matched to the detector field of view. Polarization is maintained through the assembly, and power losses are slight. Laboratory test performance is presented for both a dye laser and an excimer laser system.

Design and performance data on two laser transmitters for spaceborne laser ranging are presented. The first laser uses a master oscillator/power amplifier configuration consisting of a diode pumped Nd:YAG slab ring and a multipass diode pumped slab amplifier which can operate at 40 Hz for 109 shots. The other laser is a diode pumped Nd:YAG slab standing wave oscillator which operates at 10 Hz for 0.6 X 109 shots. For submillimeter laser ranging, one laser operates in a mode-locked cavity-dumped mode to produce 180 mJ, 40 psec pulses at 1.064 micrometers . For altimetry, the same laser operates in a Q-switched mode to produce 700 mJ, 3.5 nsec pulses at 1.064 micrometers . Second and third harmonic generators generate 0.532 micrometers and 0.355 micrometers for ranging at 2 wavelengths to terrestrial targets with inherent atmospheric correction. The oscillator utilizes a ring resonator configuration with active mode locking, active Q-switching, active pre-lase stabilization, and active cavity dumping. The mode-locked output pulsewidth is 40 psec. A second oscillator mode, remotely selectable, produces 3.5 nsec pulses. Stabilization and alignment is done with real-time feedback during the mission. The amplifier is a multipass slab. Parasitic (ASE) oscillations are suppressed despite very high stored energy in the amplifier medium. The second laser transmitter is a linearly polarized Q-switched Nd:YAG slab laser cavity. The Nd:YAG is pumped by a 44-bar array of AlGaAs laser diodes. It produces 45 mJ, 10 nsec, pulses at 1064 nm and will operate at 10 Hz for the two-earth-year on-orbit lifetime. The expected operation will produce 6 X 108 shots during the mission. The laser transmitter will consume 15 watts, which represents a 3 wall plug efficiency. The laser transmitter has a beam divergence of 0.25 mrad and will maintain boresight to the receiver within 100 (mu) rad. The lasers have been specifically developed for ultra-high reliability for use in space exploration of the earth and nearby planets. Applications include planetary altimetry of Mars (MOLA) and earth (GLRS), as well as space geodesy, navigation, and tracking.

The geoscience laser ranging system (GLRS) will be a high-precision distance-measuring instrument planned for deployment on the EOS-B platform. Its primary objectives are to perform ranging measurements to ground targets to monitor crustal deformation and tectonic plate motions, and nadir-looking altimetry to determine ice sheet thicknesses, surface topography, and vertical profiles of clouds and aerosols. The system uses a mode-locked, 3- color Nd:YAG laser source, a microchannel plate-PMT for absolute time-of-flight (TOF) measurement (at 532 nm), a streak camera for TOF 2-color dispersion measurement (532 nm and 355 nm), and a Si avalanche photodiode for altimeter waveform detection (1064 nm). The performance goals are to make ranging measurements to ground targets with about 1 cm accuracy, and altimetry height measurements over ice with 10 cm accuracy. This paper presents an overview of the design concept developed during a phase B study, under contract to NASA Goddard Space Flight Center. System engineering issues and trade studies are discussed, with particular attention to error budgets and performance predictions.

A concept for a passive multiple retroreflector target dedicated to high-accuracy laser ranging between an orbiting payload and a planetary surface is described. The target can provide, with certain field of view restrictions, good emulation of an ideal retroreflector. The described design relies on an optimization of each retroreflector in terms of the corrections for velocity aberration needed within its particular field of view, and is highly suited to systems with predictable orbital patterns.

This paper highlights some of the essential features of dual-color laser ranging, with a view of clarifying the role played by the various wavelength-dependent parameters which intervene in the overall system accuracy. Results derived from numerical simulations of link budget used to analyze the expected performance of a tuned dual-wavelength ranging system are presented.

Satellite laser ranging (SLR) has been used for over two decades in the study of a variety of geophysical phenomena, including global tectonic plate motion, regional crustal deformation near plate boundaries, Earth''s gravity field, the orientation of its polar axis and rate of spin, lunar dynamics and general relativistic studies. The subcentimeter precision of the technique is now attracting the attention of a new community of scientists, notably those interested in high- resolution ocean, ice, and land topography. Over the next several years, the international SLR network will provide an essential link between the geocentric terrestrial reference frame (as presently defined by the international VLBI and SLR networks) and two new oceanographic satellites, ERS-1 and TOPEX-Poseidon, which will range to sea and ice surfaces using microwave altimeters. The combined SLR/altimetry data set will provide precise orbits, improved gravity models, and estimates of the marine geoid. The latter are necessary to infer the dynamic sea surface topography and will enable measurements of parameters important to an understanding of global change, such as mean sea level and ice sheet thickness. Laser tracking of oceanographic satellites from multiple sites as they overfly special calibration towers equipped with tide gauges will also provide periodic estimates of microwave altimeter bias. The few-centimeter precision orbits determined by the SLR network will be used as ''ground truth'' data in the intercomparison and performance evaluation of developmental space radio-navigation systems such as GPS (TOPEX/Poseidon) and PRARE (ERS-1). Future spaceborne two-color SLR instruments, such as NASA''s geoscience laser ranging system (GLRS), can monitor the tectonically-induced motions of tide gauges by bouncing laser pulses off of collocated retroreflectors. Similar systems can measure the barometric loading over the open ocean. When used as transmitters in spaceborne or airborne altimeters, the narrow beamwidths and short pulsewidths available from lasers can provide high spatial resolution (both horizontal and vertical) topographic data over land and ice in support of a diverse set of science applications.

A narrow-beam laser altimeter was used to measure the reflected signal from the ocean surface as represented by the waters beneath the Golden Gate Bridge. This site allowed precise measurements as a function of angle from the vertical not possible from flying platforms. For short-wavelength water waves superimposed on swell, the signal amplitude probability distribution for the reflected signals showed periods of zero reflection, even for vertical incidence, apparently due to tipping of the water surface. The nonzero signals showed a distribution that could be fitted with an antilog-normal distribution. This is skewed toward higher signals than a normal (Gaussian) distribution. With incidence angle displaced from the vertical, the distribution shape was retained but with more frequent zero reflections. The decrease with angle of the average signal, including the zeroes, is well fitted with a Gram- Charlier distribution, as seen by earlier observers using photographic techniques which masked these details of the structure. For the simpler wave pattern due to a long sustained wind direction, the probability distribution is log-normal with no zero signal periods. At large angles from the vertical the log-normal distribution shifts toward exponential. For surface states intermediate between the above two extremes the distribution is often normal. The larger return signals resulting from the skew toward larger amplitudes from lognormal are more favorable for disposable laser altimeters than previously believed. Also, for an altimeter which may be swinging from a parachute or balloon, the return remains high at angles other than vertical. The presence of occasional zero return signal does somewhat degrade the accuracy of altitude measurement for a descending altimeter, but the signal available assures performance at larger altitudes than previously expected.

The relationships between percent defoliation and digital near-infrared reflectance data detected by the Landsat thematic mapper and SPOT sensors were investigated. These data were both found to be negatively correlated with defoliation data collected within the boreal montane spruce-fir ecosystem of the Black Mountains, North Carolina. Correlation coefficients were significant at the 0.05 level. Linear regression analysis demonstrated that neither source of satellite-based remotely-sensed data is an accurate predictor of defoliation. The addition of digital elevation data, however, as an independent variable to the regression equations significantly improved the predictive reliability of the models.

A highly informative content makes visible and infrared images the most used remotely sensed data (generally speaking) in earth resource and environmental analysis. On the other hand, sensitivity to surface roughness, water content, and independence of weather conditions and sunlight are the features that justify the growing interest and use of microwave radar data. The previous considerations clearly indicate data fusion as a key point for remote-sensing image classification. In this paper, a knowledge-based system to exploit such numerous and diverse sources of information is proposed. The authors started with the problem of fusing Landsat- MSS and Seasat-SAR images for terrain classification in order to increase the reliability of results with respect to single-sensor analysis. A new approach to the fusion of 2-D images, called the ''region overlapping'' technique, is employed, and its advantages for terrain classification are shown. Experimental results are presented and discussed to show the interest of the approach.

A procedure is formulated to investigate the sensitivity of surface reflectances retrieved from satellite sensor data to uncertainties in aerosol optical properties. Aerosol optical characteristics encompassed in the study include the Junge parameter (i.e., spectral dependence), the imaginary part of the refractive index (i.e., aerosol absorption), and the aerosol optical depth. Key results for a wavelength of 0.550 micrometers are presented graphically in terms of accuracy requirements on the aerosol property under consideration for a 5 uncertainty in predicted surface reflectance.

The objectives of this paper are to investigate the critical issues associated with EOS direct broadcast, and recommend design approaches for the EOS direct broadcast transmission and ground receiving. Even though the distribution of EOS data is centered around E0sDIS, there will still be strong needs for direct broadcast for the following reasons: TDRSS backup in case of system unavailability, provision of data for real-time or near real-time applications in regions around the world, transmission of data to remote sites to support field experiments and/or operational activities, development of the next generation direct broadcast service Some of the critical design issues associated with EOS direct broadcast are: 1) the choice of data subsets for direct broadcast, 2) the mode of transmission, 3) impacts on power, mass and cost, 4) the design of ground stations, and 5) the feasibility of on-board processing for direct broadcast. We envision two categories of direct readout stations. United States and nations such as Australia, Canada and China, which have or will have LANDSAT class ground stations, belong to the first category. These stations can support a data-rate of up to 100 Megabit per second (14bps). The second category includes smaller nations, like Indonesia, Bangladesh, Pakistan, and some African nations, which have or will have TIROS HPRT class ground stations. With some upgrades (mainly in the antenna and tape-recorder), these stations can receive a data—rate of up to 10 14bps.

The computational workload of upcoming NASA science missions, especially the ground data processing for the Earth observing system, is projected to be quite large (in the 50 to 100 gigaFLOPS range) and correspondingly very expensive to perform using conventional supercomputer systems. High-performance, general-purpose, massively-parallel computer systems such as the MasPar MP-1 are being investigated by NASA as a more cost-effective alternative. Massively parallel systems are targeted for accelerated development and maturation by NASA''s upcoming five-year High Performance Computing and Communications Program. A summary of the broad range of applications currently running on the MP-1 at NASA/Goddard are presented in this paper along with descriptions of the parallel algorithmic techniques employed in five applications that have bearing on earth sciences.

Xybion Corporation has developed an airborne multispectral measurement system (AMMS) as part of a small business innovative research contract with the Department of Commerce. The AMMS is a low-cost portable system that can provide multispectral data suitable for frequent measurement and mapping. It has been used for measurement of estuarine concentrations of chlorophyll and suspended sediments and mapping of submerged aquatic vegetation fields. Other applications include the identification of tree and plant species, the detection of crop stress, and the detection of man-made objects in a background of vegetation. The AMMS provides high spatial resolution multispectral image data in six user-defined bands in the 400- 900 nm wavelength region. The AMMS includes a highly innovative, computer-controlled, intensified, multispectral video camera (IMC), a spectroradiometer, a S-VHS VCR, and a portable IBM-PC-compatible computer system. An airborne trial over Cheseapeake Bay in June 1990 showed its ability to detect variations in water parameters. Simultaneous measurements from a ship provided sea-surface data, including continuous fluorometer readings, and discrete samples of chlorophyll, suspended sediments, and several other water parameters. Two spectroradiometers were included in the airborne equipment. One pointed downward to provide a high-resolution spectrum of a large water area under the plane. The other spectroradiometer measured downwelling irradiance. This allowed for conversion of the upwelling radiances measured by the IMC into reflectances. Calibrations for the IMC and the spectroradiometers were done before and after the trials. The results of this airborne trial are presented.

The U.S. Army Corps of Engineers, U.S. Fish and Wildlife Service, and the Environmental Protection Agency are charged with the responsibility to jointly manage the nation''s wetlands in accordance with the Clean Water Act and the Rivers and Harbors Act. The Corps'' role is enforcement of regulations concerning dredging and filling of specific types and areas of wetlands that fall within jurisdictional boundaries. Current research is being conducted to enhance the field scientist''s ability to manage these ecosystems using digital aerial photography, image processing, and photo interpretation logic. This paper presents techniques used to scan (digitize), archive, and utilize digital aerial photography for environmental resource management using a photogrammetrically accurate, CCD-based scanner. Spectral characteristics of the imagery and useful image processing routines to enhance the resulting raster file(s) for interpretation are discussed.

Automated multispectral band selection facilitates access to meteorological information in satellite images. Computed quickly and automatically, multispectral band triplets having the least interband redundancy produce vivid color displays bearing the highest information potential. Results from a 12-band multispectral data set collected in spring near Bridgeport, California show that a combination of near-infrared (0.91 - 1.05 micrometers ), shortwave infrared (2.08 - 2.35 micrometers ) and longwave infrared (8.5 - 14.0 micrometers ) produces minimum interband redundancy. The automated method, which features simple manipulations of the spectral band correlation matrices, appears to be computationally robust and adaptable to changes in image scenery.

There will be several state-of-the-art spectrometers in operation on the NASA Polar Orbiting Platform (NPOP-1) as part of the Earth observing system (Eos). The moderate resolution imaging spectrometer (MODIS) will consist of two imaging spectroradiometric instruments, one nadir viewing (MODIS-N) and the other tiltable (MODIS-T), for ocean observation and land bidirectional reflectance studies. The moderate resolution imaging spectrometer-tilt (MODIS-T) instrument is presently being constructed for flight on the EOS. It is an imaging spectrometer utilizing a grating type, reflecting Schmidt optical design that must provide a 1.1 km cross-track swath and a +/- 50 deg forward and aft tilt capability. The instrument is required to cover the wavelength range from 400 to 880 nm in approximately 15 nm steps with less than 2.3 instrument induced polarization. The absolute radiometric accuracy must be at least 5 over the full dynamic range of the instrument.

Tropical radar environmental information system (TREIS) is a concept for a system of tropical forest monitoring based on satellite radar remote sensing. The approach is novel--starting from the ground up. TREIS offers a way around three major obstacles that are likely to preclude large-scale use of currently planned space radars: (1) high primary data cost; (2) complex and centralized ground segment infrastructure; and (3) a less than optimum radar wavelength. The proposed system is specified based on existing regional capabilities in data reception, processing, and utilization. The space segment uses existing AVHRR class data telemetry (625 Kbps), and partial on-board preprocessing of the P-band (75 cm) synthetic aperture data. Aggregate coverage of the earth''s tropical forests twice a year is achieved with ten look imagery of 20 km usable swath width and pixel spacing of 50 m. Image processing requires only work stations or high-end PC-class hardware which could be distributed over many regional centers. Data products could be prepared rapidly and inexpensively for regional use and for global inventory efforts such as those of the United Nations.

The potential of using remote sensing for the detection of chlorophyll-a (CHL), dissolved organic matter (DOM), and suspended matter (SM) concentrations in coastal and inland waters was investigated using near-surface measurements of upwelling and downwelling (IR) radiance spectra along with simultaneous earth-reference data obtained on the test areas. The range of CHL was 0.1 to 350 (mu) g/l, suspended matter was 0.1 to 43 mg/l, and DOM absorption at the analyzed wavelength (380 nm) was 0.1 to 10-1. Factor and signature analysis reveal allometric relationships between constituent concentrations Ck and functions of reflectance Zk of the type Ck equals aZkb. Appropriate functions of reflectance were found for the different constituents to be: Zchl1 equals R(700)/R(675), Zchl2 equals R(700)/R(560), and Zchl3 equals [R(700)-R(675)]/[R(700)+R(675)]; and Zsm1 equals [R(560)-R(520)]/[R(560)+R(520)], Zsm2 equals R(560)/R(520); and Zdom equals {R(480)+k[R(700)/R(675)]}/R(630). The maximum estimation errors were: CHL - 3 (mu) g/l, DOM - 0.065 (mu) gC/l, and SM - 4 mg/l. The parameters a and b differ significantly over different water areas for CHL, but this can be adjusted by virtue of good correlation with the averaged local value of CHL (Cchlavg). By using local correction, as in the equation Ck equals a(Cchlavg)Zb(Cchlavg), it is possible to detect CHL in water areas of different trophic states with estimation errors varied between 1.75 and 8.34 (mu) g/l. There is a wide range of wavelengths over which a simple reflectance function Z equals Ri/Rj works quite well for CHL, permitting use of even such wide-band sensors as MSS Landsat. Band combinations MSS6/MSS4 and MSS6/MSS4 + 5 + 6 are suitable for remote sensing of CHL if the value of Cchl ch

Experimental results on remote sea sensing from a research vessel by wavelength tunable lidar with a multichannel optical detector are given. The performances of the spectral signatures method for diagnostics of water media containing phytoplankton pigments, dissolved organics, oil pollutants at low concentration levels, etc., are discussed.

High-quality multispectral images in the visible, near-infrared, shortwave infrared, thermal infrared, and microwave regions of the electromagnetic spectrum were acquired of the extreme north end of Death Valley, California/Nevada, during a multisensor aircraft campaign called the Geologic Remote Sensing Field Experiment (GRSFE) conducted during 1989. The airborne data sets include the airborne visible/infrared imaging spectrometer (AVIRIS) (0.4 - 2.5 micrometers , 224 bands), the thermal infrared multispectral scanner (TIMS) (8-12 micrometers , 6 bands) and the airborne synthetic aperture radar (AIRSAR) (P, L, and C band, quad polarization, multiple incidence angles). Ancillary data include Landsat multispectral scanner (MSSS), Landsat thematic mapper (TM, 7 bands), a digital elevation model (DEM), laboratory and field spectral measurements, and traditional geologic mapping. The image data sets were used to produce thematic image-maps showing details of the surface geology. Landsat TM images were used to map the distribution of the broad mineral groups of clays/carbonates and iron oxides. AVIRIS data permitted identification and mapping of specific minerals (calcite, dolomite, sericite, hematite, and goethite) and some mixtures. TIMS data were used to map the distribution of igneous rock phases based on their silica contents, and carbonates. AIRSAR data were used to identify and map the scale of surface roughness. The AIRSAR data also allowed identification of previously unmapped fault segments and structural control of lithology and alteration mineralogy. Because all of the above data sets were geographically referenced, they could be easily used for integrated analysis and results from the different sensors could be directly compared.

The Geologic and the National Mapping Divisions of the U.S. Geological Survey have been involved formally in cooperative research and development of computer-based geographic information systems (GIS's) applied to mineral-resource assessment objectives since 1982. Experience in the Conterminous United States Mineral Assessment Program (CUSMAP) projects including the Rolla, Missouri; Dillion, MT-ID, Butte, Montana; and Tonopah, Nevada, 1° x 2° quadrangles has resulted in the definition of processing requirements for geographically, and mineral-resource data that are common to these studies. The diverse formats of data sets collected and compiled for regional mineral-resource assessments necessitate capabilities for digitally encoding and entering data into appropriate tabular, vector, and raster subsystems of the GIS. Although many of the required data sets are either available or can be provided in a digital format suitable for direct entry, their utility is largely dependent on the original intent and consequent preprocessing of the data. In this respect, special care must be taken to ensure that digital data type, encoding, and format will meet assessment objectives. Data processing within the GIS is directed primarily toward the development and application of models that can be used to describe spatially geological, geophysical, and geochemical environments either known or inferred to be associated with specific types of mineral deposits. Consequently, capabilities to analyze spatially, aggregate, and display relations between data sets are principal processing requirements. To facilitate the development of these models within the GIS, interfaces must be developed among vector-, and raster-, and tabular-based processing subsystems to reformat resident data sets for comparative analyses and multivariate display of relations.

In this paper a novel approach to high-resolution infrared atmospheric temperature sounding by using the multi-order etalon sounder (MOES) is discussed. The MOES exploits the periodic characteristics of Fabry-Perot interferometer (FPI) transmission function and the uniform line spacings of CO2 to maximize the instrument signal and to achieve the high-spectral resolution needed to improve the vertical resolution and retrieval accuracy of atmospheric temperature sounding. In this paper the MOES technique and a conceptual instrument design are presented. Suitable CO2 spectral regions, optimum etalon-free spectral ranges, characteristics of 44 representative temperature sounding channels and 12 water vapor sounding channels are calculated and discussed. Performance simulation studies indicate that MOES can provide more accurate temperature and water vapor profiles than the current operational high resolution infrared sounder (HIRS/2). The improvement in temperature and moisture retrieval accuracy with MOES is mainly due to its higher spectral resolution and the ability to resolve a single CO2 spectral line.

The 24-channel Geoscan scanner includes six grating-dispersed thermal infrared channels, co- registered with the 18 VNIR and SWIR bands. Considerable silicate (hydroxyl) discrimination can be seen in the SWIR band images but will not be treated further in this paper. Each of the TIR bands has a bandpass of 530 nm, centered between 8.64 and 11.28 micrometers band centers dispersed onto a linear detector array of HgCdTe. The system has been flown over Ludwig, Nevada three times (May 1989/June 1990), and twice over Virginia City, Nevada (June 1989/Aug. 1990). Pixel sizes ranged from 3 m to 6 m in this ''research-mode'' flying. In flight the scanner is operated in a noncalibrated, relative-radiance mode in all of the 24 channels. A sample of the terrain to be mapped is overflown, during which the offsets of each channel are set to mid-range (DN equals 127), with the data spread by the gain setting so as to occupy all of the 8-bit range. The recording therefore is of the 8 bits of data spread about the average (relative) brightness of the terrain in that band. In this manner, this scanner differs from almost every other unit either in airborne use or in the Landsat satellites. These units record absolute brightness from which, by use of the calibration parameters, the absolute radiance of the terrain may be reconstructed. The problem is to perform a transformation of the imagery to apparent reflectance allow comparison of the spectra extracted from the airborne imagery to ground-measured spectra. TIR spectra have also been obtained in ground-based stationary laboratory-type operation of the aircraft scanner, viewing warm samples (heated by the sun to about 45 C) for fifteen of the major rock-type assemblages. These laboratory-scanner match the airborne-scanner spectra abstracted from the imagery data as well as direct exitance spectra obtained previously from other sun-warmed samples.

Stratigraphic and structural studies of the Wind River and Bighorn basins, Wyoming, and the Guerrero-Morelos basin, Mexico, have resulted in development of ''spectral stratigraphy.'' This approach to stratigraphic analysis uses photogeologic and spectral interpretation of multispectral remote sensing data combined with topographic information to determine the attitude, thickness, and lithology of strata exposed at the surface. This paper reviews selected published examples that illustrate this new stratigraphic procedure. Visible to thermal infrared laboratory, spectral measurements of sedimentary rocks are the physical basis for spectral stratigraphy. Results show that laboratory, field, and remote spectroscopy can augment conventional laboratory and field methods for petrologic analysis, stratigraphic correlation, interpretation of depositional environments, and construction of facies models. Landsat thematic mapper data are used to map strata and construct stratigraphic columns and structural cross sections at 1:24,000 scale or less. Experimental multispectral thermal infrared aircraft data facilitate lithofacies/biofacies analyses. Visible short-wavelength infrared imaging spectrometer data allow remote determination of the stratigraphic distribution of iron oxides, quartz, calcite, dolomite, gypsum, specific clay species, and other minerals diagnostic of environments of deposition. Development of a desk-top, computer-based, geologic analysis system that provides for automated application of these approaches to coregistered digital image and topographic data portends major expansion in the use of spectral stratigraphy for purely scientific (lithospheric research) or practical (resource exploration) objectives.

The NASA thermal infrared multispectral scanner (TIMS) has been successfully used for the remote identification of a variety of soil and aggregate deposits in vegetated areas of two states. Over three million cubic meters of gravel deposits were identified from the imagery during a two-year period. Verification was accomplished by ground reconnaissance using drilling machinery provided by the United States Forest Service (USFS), and by ground instrumentation provided by NASA''s Science and Technology Lab. (STL). The method has been used to differentiate between fine- and coarse-grained soils, and gravel deposits. The deposits were found to have been naturally sorted according to grain size by depositional processes, providing each deposit with distinct spectral qualities. It was found that the masking effects of relatively dense vegetation were largely overcome by using imagery acquired at higher altitudes above terrain than 9000 m, due to loss of resolution of the finer detail. The mechanics of image resolution are discussed, a method of data analysis is described, and sample spectral signatures are illustrated.

A variety of new approaches to the global detection and monitoring of geological hazards will be available as a number of new earth-orbiting satellite systems become operational toward the end of the current decade. These involve (a) multi-instrumented low-earth orbital platforms such as the Eos Mission (b) multi-instrumented geostationary research platforms and (c) small single-instrument low-earth orbiters. The capabilities of these platforms combined with greater spectral range and higher spatial and spectral resolutions will provide data appropriate to the detection and monitoring of many transient geological hazard phenomena. Improved worldwide communications and international cooperation will be necessary to take advantage of this emerging operational technology.

A new type of Fabry-Perot Interferometer (FPI) which exploits the multiplex advantage is presented. The Multiplex Fabry-Perot Interferometer (MFPI) has one etalon plate that is fixed while the other is moved over a large optical distance thus producing an interferogram similar to that obtained with a Michelson Interferometer. The result is an instrument which has the ability to examine large spectral regions at high resolution using the inversion techniques normally applied to a Michelson Interferometer while retaining the small size of an FPI. The MFPI is a compact rugged high resolution instrument that will be useful for the remote sensing of minor species.

Remote sensing is playing an increasingly important role in management and development of coastal environments through the detection and monitoring of coastal processes. Coastal geomorphic changes, estuarine circulation, pollution and sediment transport, flood area extent, fires, and foliage die-back are readily detectable from aircraft and spaceborne sensors. These data have their greatest value when they are available in near real-time to decision makers such as civil officials (crisis response), corporate officials, and coastal/marine environment operators. Examples of flooding, fires, storm-driven and man-induced damage to coastal environments graphically illustrate the dynamics of these environments. This paper illustrates how a low-cost NOAA high resolution picture transmission (HRPT) earth station provides technological leverage to deal with some of them.

The Alaskan eruptions of Augustine Volcano (1986) and Redoubt Volcano (1989-90) were major hazards to air traffic at Anchorage, along a major polar air route. Detailed examinations were made of multispectral imagery collected by the advanced very high resolution radiometer (AVHRR) aboard polar orbiting NOAA weather satellites. More than 70 images of eruptions from the two volcanoes, which exhibit a great variety of eruptive and atmospheric conditions have been examined. The data set offers an elaborate test of the utility of synoptic weather satellites for discriminating and tracking eruption clouds. The results so far are very encouraging, demonstrating a success in discrimination and mapping of eruption clouds under a variety of conditions. The two eruptions have different spectral characteristics, which have precluded the use of a single algorithm to discriminate eruption clouds from meteorological ones. Laboratory spectral study of ashes collected from the field are being used to help understand differing spectral characteristics of ash clouds as detected by the AVHRR.

The moderate resolution imaging spectrometer (MODIS) is an earth-viewing sensor that is planned as a facility instrument for the Earth observing system (Eos) scheduled to begin functioning in the late 1990s. The MODIS is composed of two mutually supporting sensors, one of which is MODIS-T (where ''T'' signifies a tiltable along-track field of view). MODIS-T is a 32-channel imaging spectrometer with a required 10 nm to 15 nm spectral resolution (FWHM) in the 400 nm to 880 nm spectral range with less than 2.3 instrument-induced linear polarization. At nadir the instrument provides a 33 km by 1500 km swath with a 1.1 km spatial resolution and an along-track pointing capability of +/- 50 degree(s). The heart of the optical design consists of a f/3 grating-type reflecting Schmidt camera.

Satellite-derived imagery can be used to measure subresolution horizontal terrain displacements associated with present-day earthquakes. This constitutes a new use of these data and may ultimately provide a unique capability for deriving spatially-comprehensive maps of local subaerial crustal deformation worldwide.