A new method has been developed for the global assessment of trace gases and particulates emission from tropical biomass burning. The method is based on remote sensing of one emitted product - particulates. It uses daily meteorological satellite data with resolution of one km2. The visible (0.63 rim) and near Infrared (0.84 rim) bands are used to determine the mass of particulates in the emitted smoke and to estimate the relative contribution of flaming and smoldering fires to the resulting smoke. The mid-IR (3.5-3.9 rim) and the thermal infrared (1 0.5-1 1 .4 ji.m) bands are used to detect and count fires in order to integrate the smoke result with the whole season and for the whole area of interest. The thermal channels are sensitive enough to detect flaming fires as small as lOm*lOm and smoldering fires as small as 30m*30m. The detected mass of emitted particulates is converted into a mass of emitted trace gases using published relations between the emitted particulates and trace gases for the flaming and smoldering phases. The.technique can be applied to regions where intensive biomass burning takes place. It is capable of monitoring the extent of current biomass burning, to discover new deforestation frontiers (unknown otherwise), and to estimate quantitative contribution of biomass burning to changes in atmospheric composition. The method has been applied to a limited area where substantial deforestation has taken place. Analysis of the 1987 burning season shows that in Brazil (in a limited area between 6.5-15.5 south and 55-67 west) during the three months of the dry season (July 1 till Sept. 30) there are up to 8000 fires a day (observed from space) each contributing 4,500 tons of C02, 750 tons of CO and 26 tons of CH4 to the atmosphere. During the dry season of 1 987, it is estimated that 240,000 fires were burning in this area resulting in the emission of 1.1013 of particulates, 71 012 g of CH4, 21 014 g of CO and 1 •1 015 g of CO2. A comparison to estimates of global emissions is also given.

Simple time integrations of AVHRR/NDVI have been correlated with annual net primary production of terrestrial vegetation; yet this implies seasonally constant physiological efficiency of the vegetation. We present logic for a time integrated NDVI that is modified by an AVHRR derived surface evaporation resistance factor a, and truncated by temperatures that cause plant dormancy, to improve environmental sensitivity. With our approach, NDVI observed during sub-freezing temperatures is not integrated. Water stress related impairment in plant activity is incorporated by reducing the effective NDVI at each integration with the surface resistance factor, a. The surface resistance factor is derived from the slope of the surface temperature to NDVI ratio for climatically similar zones of the scene. A comparison of surface resistance before and after an extended drought period for a 1200km2 region of coniferous forest in Montana will be presented.

The global water cycle is perhaps the most important of all the biogeochemical cycles and evaporation, which is a significant component of the water cycle, is also linked with the energy and carbon cycles. Long-term evaporation over large areas has generally been computed as the difference of precipitation and river runoff. Analysis of short-term evaporation rate and its spatial pattern, however, is extremely complex, and multispectral remotely sensed data could aid in such analysis. Multispectral data considered here are visible and near-infrared reflectances, infrared surface temperature and the 37 GHz brightness temperatures. These observations are found to be not totally independent of each other. A few of their relationships are established and discussed considering physically-based models.

Field measurements of primary production in semi-arid grasslands in three Sahelian countries over a period of eight years are analyzed in conjunction with multitemporal sums of vegetation indices derived from the NOAA spacecraft's Advanced Very High Resolution Radiometer. The results demonstrate that there is a strong linear relationship between the satellite observations of vegetation indices and the prlmaiy production in the range 0-3,000 kg ha. The confidence intervals of estimation of production were in the range ±61-161 kg ha.

The functional relation among subpixel canopy cover, illuminated soil, and shadowed soil, which progressively develops with increasing pixel size, is investigated for Poisson distributed plants using a geometric canopy simulation model. An analytical relation among cover components is shown to be applicable when the scale of the pixel is much larger than the scale of the plant and ground shadow. The analysis is facilitated through the use of a nondimensional solar-geometric similarity parameter, r, equal to the ratio of the area of one plant canopy to its associated ground shadow area, as viewed from nadir. Use of the similarity parameter generalizes the results without constraining them to any one geometric shape or solar angle. A Sampling Scale Ratio, defined as the ratio of the area of the pixel to the mean area of a single plant shadow, is tested as a quantitative criterion to evaluate when the functional relation among subpixel components occurs. The results of a remote sensing experiment over a natural conifer landscape provide preliminary confirmation of the theoretical analysis.

An objective of NASA's Biospheric Research Program is to understand biogeochemical cycling on a global scale. Being both very biologically productive and anoxic, wetlands are major sites of carbon dioxide, mean, and sulfur gas flux on a per area basis. Biogeochemical cycling in wetlands is intricately linked to vegetation biomass production. We have been monitoring biomass dynamics of the dominant salt marsh grass Spartina alterniflora for over ten years using remote sensing. Live above ground biomass is highly correlated (r = .79) with Laridsat Thematic Mapper ('IN) and SPOT spectral data transformed into normalized difference vegetation indices. Live belowg round biomass is, in turn, highly correlated (r = .86) with live above ground biomass. Therefore, below ground biomass, a source of carbon substrates for microbial gas production, can be measured using remote sensing indirectly. These relationships have been tested over a wide latitudinal range (from Georgia to Nova Scotia). Analysis of TM and SPOT satellite images from several years has revealed substantial interannual variability in mean live aerial biomass of this species in a 580ha Delaware marsh. Additionally, interannual spatial variability in biomass distribution within the marsh is evident and seems to be linked to precipitation. The aerial biomass of high salinity areas least influenced by upland runoff is the most sensitive to precipitation, whereas marsh areas adjacent to large upland areas or freshwater creeks are the least sensitive. In summary, remote sensing is an effective tool for studying aboveground and belowground biomass in salt marshes. Once the relationship between gas flux data and vegetation biomass is better understood, satellite data could be used to estimate biomass arid gas flux over large regions of the world.

The SASWG [SST (Sea Surface Temperature) Archiving Science Working Group], formed in early 1987 by NASA and NOAA, suggested production of two classes of SST products to meet the needs of the scientific community: SST fields addressing the needs of feature-related studies, and SST values accompanied by ancillary spectral and geometric parameters addressing the needs of heat flux related studies. Following the recommendations of the SASWG, NASA identified a smaller group to define the steps required to produce the feature-related product and to begin execution of the first steps. The underlying assumption in beginning this effort was that the required fields could be produced, as suggested by the SASWG, from the global GAC (Global Area Coverage) AVHRR/2 data set that extends from June 1981 to present. In that interests within the terrestrial community for global vegetation maps using the portion of GAC data covering the continents could be met with the same data stream, NASA also suggested integrating the production of the feature-related SST fields and the vegetation index. The perceived benefit is that, in addition to making these fields available to the research scientists in both communities, the integration of the production of these fields will serve as an excellent prototype for the production of interdisciplinary fields that must be undertaken as part of NASA's EOS effort. This manuscript deals with considerations going into defining the feature-related products, the steps outlined for their actual production, and the progress made thus far.

The study of the Earth's climate system is now an important central focus for the new discipline of Earth Science. Simulation models, particularly General Circulation Models (GCMs), of the atmosphere are essential tools for the global change research effort as they allow the detailed investigation of the mechanisms involved and offer some promise for predicting the Earth systems' response to perturbation.

Flux measurements of water vapor and sensible heat, using aircraft-mounted sensors, have been obtained by several research groups during the last two decades. More recently, CO₂ flux, as well as radiative data from aircraft and satellite measurements, have also been obtained in conjunction with such fluxes. The combination of these data provides an excellent opportunity for developing an improved understanding of terrestrial ecosystem-atmosphere interactions which has become an important challenge if we are to assess correctly man's impact on the atmosphere and climate. This paper will attempt to demonstrate the current status of airborne flux measurements in North America for obtaining large area estimates of surface fluxes.

The HAPEX-DBILHY program is studying the hydrological budget arid evapotranspiration (ET) flux at the scale of the GG4 grid square i.e. 1O⁴km². For the program several surface and subsurface networks operated from mid 1985 to early 1987 to monitor soil moisture, surface energy budget, and surface meteorological parameters. During the Special Observing Period (SOP) from 7 May to 15 July 1986, there were additional measurements including detailed observations of atmospheric fluxes at the surface and with two well instrumented aircraft: the NCPR King-Air for eddy correlation flux measurements and the NTSA C-l30 for remote sensing observations. Brief descriptions of measurement systems and some results from the SOP will be presented here concentrating on the remote sensing of surface tetrerature.

An extensive multisensor airborne and field campaign was conducted in the Northern Experimental Forest near Bangor, Maine, during September 1989 to acquire a data set to allow us to test various modeling hypotheses concerning the interaction of optical, thermal, and microwave electromagnetic radiation within northern coniferous forest canopies and their underlying backgrounds. This experiment represents a significant component of a Forest Ecosystem Dynamics project, which is concerned with the response of northern forests to climatic and other environmental changes. Extensive ground control information, basic remote-sensing measurements, and comprehensive calibration data were obtained to support the interpretation of numerous airborne sensor measurements and to provide both static and dynamic biophysical input parameters to electromagnetic scattering and absorption models. Aircraft instruments deployed included a multifrequency, quadpolarized synthetic aperture radar, a solid-state array bidirectional imager, and the Thematic Mapper Simulator. In addition, a suite of helicopter-borne nonimaging systems was utilized, consisting of a multifrequency laser polarimeter and both narrow- and broad-band spectrometers. This paper presents background on this first Forest Ecosystems Dynamics field campaign, provides a progress report on the analysis of the collected data and related modeling activities, and outlines plans for future experiments at different points in the phenological cycle.

The Earth Observing System (EOS) is a key element of the U.S. Program in Global Change. It is NASA's initiative to provide the scientific means to observe the earth as a system. The EOS satellite system and accompanying Data and Information System (DIS) provide spacebased platforms and groundbased elements for scientific research and information extraction. The program recognizes the need for global coverage, long term observations, and multidisciplinary analyses in order to detect subtle changes in the environment's state. A multidisciplinary payload of active and passive sensors is proposed to accomplish the objectives of the program. International partners are an important element of the program. This paper focuses on the instrument complement for the EOS-A spacecraft since those decisions will occur this year. Significant programmatic constraints and program science decisions will impact the selection of the EOS-A payload.

The Moderate Resolution Imaging Spectrometer-Nadir (MODIS-N) for the Earth Observing System (EOS) is intended to provide daily global surveys for the atmosphere, the oceans, and the land. To achieve this capability, MODIS-N requires an at-least 2300-km swath width, and provides geometric-instantaneous-fields-of-view (GIFOVs) that are either 856 m, 428 m, or 214 m in size with reference to a 705 km satellite altitude. The 214 m GIFOV may or may not be used depending on total data rate impact assessments traded with science needs. To achieve the data for the multiplicity of science investigations MODIS-N provides nominally 36 spectral bands that are selected for specific locations and bandpasses in the spectral range from the visible to the long wave infrared. Another driver of this instrument combination is the need for long term spectral and radiometric calibration stability. Specific calibration capabilities are to be built into MODIS-N to achieve calibration knowledge over a 5 year operational life.

The Atmospheric Infrared Sounder (AIRS) is a grating-array spectrometer on EOS. It covers the region from 650 to 3000/cm with spectral resolution of 1200. The prime objective of AIRS is the global retrieval of temperature and water vapor profiles and of surface temperatures. The wide spectral coverage of AIRS permits the measurement of a number of additional atmospheric and surface parameters. Of particular interest is the potential to produce daily global maps of the spatial distribution of the more abundant of the minor gases, e.g. ozone, CO, CH4, and N2O. This potential capability for CH4 and N2O is strongly affected by cloud residual. Using the CH4 band at 1306/cm as example, spatial averaging of AIRS data is required to measure a 10 percent change in the nominal CH4 column abundance. At 1300/cm, this requires cloud clearing at the 0.3 percent level. The mapping capability for ozone and CO in terms of rural/urban abundance patterns is not likely to be impacted with cloud-clearing residuals as high as 5 percent.

The Multi-angle Imaging SpectroRadiometer (MISR) experiment is an Instrument Investigation in the planning stages for the first NASA Earth Observing System polar platform, EOS-A. MISR will routinely acquire multispectral images of the angular reflectance signatures of terrestrial scenes. Scientific objectives include study of the climatic and environmental impacts of atmospheric aerosols, characterization of heterogeneous cloud fields and their impact on the shortwave radiation budget, development of surface bidirectional reflectance and albedo models for land surface climatology studies, and investigation of biosphere-atmosphere interactions and ecosystem change. This paper describes the MISR investigation, instrument, and data products.

The requirements for characterization and calibration of instruments for the Earth Observing System space segment are defined in terms of tracking the Level 1 data for a sensor. The data must be traceable over the 15 year program, and must provide corrections for radiometric, spectral and geometric coefficients which capture the combined design and performance characteristics of the sensor. These requirements are then developed for MODIS-N to identify a set of techniques which can be used in the laboratory, spacecraft integrator's facility and in-orbit. The in-orbit of the so-called reflectance and radiance methods are reviewed, and the cross-calibrations available between HIRIS and MODIS through these techniques are listed. A scheme for the use of all available tools for instrument performance is provided as a Figure showing an estimated time interval over which each tool is expected to be useful. The final calibration strategy and plan must be developed through the understanding of a useful strategy for each of these candidate mechanisms.

Current trends in the development of optical imaging systems are reviewed, along with the demands for future improvements in the areas of resolution, the range of coverage, narrowing individual wavebands, simultaneous imaging, stereoscopic color imaging, and shortening of imaging intervals. A method of high-resolution stereoscopic imaging utilizing wide-zone coverage and data compression is proposed. It is pointed out that a conceptual system would be an extension of the wide-zone imaging function provided by an aspherical optical system with multiple electronically switched CCDs mounted on the focal plane. The data compression is discussed in detail, and it is noted that with optical sensors incorporating multiple CCDs, the best results can be obtained by using the inter-line correlation as data for deriving forecast values. Future high-resolution intelligent imaging systems are discussed.

This paper describes the algorithms and procedures used for in-flight calibration of the nonscanning radiometers used in the Earth Radiation Budget Experiment (ERBE) instruments. The computation of the count conversion coefficients used in the basic ERBE radiometric equations is described, as well as the determination of the offsets and time-dependent coefficients used to account for the in-flight changes in the radiometers. The calibration results for more than 5 years of ERBE data are summarized for all nonscanning radiometers. Discontinuities in the observed data, and the effects of these discontinuities are discussed. Applications of ERBE type calibration algorithms to the EOS/CERES platforms are suggested.

There will be several state-of-the-art spectrometers in operation on the NASA Polar Oribting Platform (NPOP-1) as part of the Earth Observing System. 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 MODIS-T instrument is required to cover the wavelength range of 400 to 880 nm in approximately 15 steps, have less than 2.3 percent instrument-induced polarization, be calibrated to an absolute radiometric accuracy of at least 5 percent over the full dynamic range of the instrument, have a 1.1 kilometer square instantaneous field of view at nadir, and be capable of + or - 50-deg along-track tilt.

The study is based on a premise that if the polarization information from the reflected radiation is extracted by an imaging polarimeter, it is possible to reveal details about the surface that are not obtainable by other imaging techniques. A polarimetric analysis system is expressed mathematically, and the resulting mathematical notation taking into account the effects caused by rotation of the various optical elements is derived. A basic system design consisting of an optical, sensor, polarimeter control, and image processing subsystems is presented. Computer analysis of the optical components is used for the optimization of the complete optical system. By including a filter, quarter-wave plate, and dichroic polarizer in the analysis, prediction of the focusing requirements of the system is made possible. Results of laboratory-based experiments are assessed.