Suraiya P. Ahmad

Temporal attributes of the bidirectional reflectance for three boreal forest canopies

Multidirectional ground-based optical measurements were acquired along tramways above and beneath three important boreal forest canopies to characterize the complete radiative transfer of visible through shortwave infrared wavelengths. The three forest canopy types exhibited bidirectional reflectance features that were distinctively different from each other not only in their magnitudes of reflectance in a given spectral wavelength band and at forward and backscatter angles but also in their diurnal and seasonal changes. The above-canopy data analyses indicate that each of these forest types must be considered as having unique bidirectional reflectance distribution functions and should be modeled individually for both direct (e.g. albedo) and indirect (e.g. biophysical parameter assessments) applications in the quantitative remote sensing of the boreal forest biome.

Radiometric Calibration Of The Reflective Bands Of NS001-Thematic Mapper Simulator (TMS) And Modular Multispectral Radiometers (MMR)

A primary goal of the radiometric calibration efforts for the First ISLSCP (International Satellite Land Surface Climatology Project) Field Experiment (FIFE) is to provide consistent radiometric calibration of the NASA-provided aircraft and field instruments, particularly in the reflective (solar) portion of the spectrum. To this goal, a common source and traceability were chosen for use by all instruments for the primary calibrations: a 122 cm diameter hemisphere maintained by the Standards and Calibration office at GSFC. Among the primary multispectral reflective band instruments used in FIFE are the NS001 scanner on a C130 aircraft operated by Ames Research Center and several Barnes Modular Multispectral Radiometers (MMRs) operated on a helicopter and the ground. These instruments have 7 bands in the reflective portion of the solar spectrum: approximately the TM bandpasses and an additional band at about 1.2 um. The NS001 has a continuously variable gain setting; calibration is maintainable only by reference to its internal light source. Calibration of the NS001 data is affected by drift in the dark current level of up to 6 counts during a mirror scan at typical gain settings. Use of both samples of the dark current recorded by the instrument in performing the calibration, as opposed to the one currently used, generally decreases the uncertainty to less than 1 count, with the possible exception of channel 7. The apparent radiance of the internal source degraded an average of 4% over the 11 month period of January 1987 to December 1987 relative to the 76 cm sphere used to monitor it; this 76 cm source in turn apparently degraded 5-10% during the same period, suggesting an overall 10-15% degradation in the internal source. The MMR instruments are being used in their 1° degree field-of-view (FOY) configuration on the helicopter and 15° FOV on the ground. Pre- and post-season laboratory calibrations were supplemented by daily stability checks using a 30 cm integrating sphere source. The changes in calibration of the MMR instruments were related to the extent of their use. In the silicon channels of the MMRs , instruments used throughout the 4 field campaigns showed degradations of 3-4% between pre- and post-season calibrations; the one instrument used for 2 of the field campaigns degraded approximately half those values; and the instrument used just one day showed pre- and post-season calibrations within one percent of each other. Strong temperature sensitivity in the lead-sulfide channels (PbS) channels, about ±25% over a 15° C range, which was reduced to ±4% or less with temperature correction, led to greater uncertainty in these channels calibration, although pre- and post-season calibrations differences were no larger than for the silicon channels.

Atmospheric Products from the Ozone Monitoring Instrument (OMI)

Ozone Monitoring Instrument (OMI) is a Dutch-Finnish ozone monitoring imaging spectrometer that is designed to provide accurate measurements of total column ozone, ozone profile, surface UV irradiance, aerosols and cloud characteristics, and the column amounts of trace gases SO2, NO2, HCHO, BrO, and OClO at high spatial resolution. The OMI along with the three other instruments, the Microwave Limb Sounder (MLS), the High Resolution Dynamics Limb Sounder (HIRDLS), and the Tropospheric Emission Spectrometer (TES), will be flown on the NASA’s Aura mission in early 2004. The standard atmospheric chemistry and dynamics products derived from OMI, MLS, and HIRDLS will be archived at the NASAs GES DAAC (TES data products will be archived at NASA Langley Research Center DAAC) and will be freely available to the public. Highlights of OMI data products, as well as their availability, distribution and data support are discussed in this paper.

Radiometric calibration of a polarization-sensitive sensor

The radiometric accuracy of a sensor is adversely affected by scene polarization if its optical system is sensitive to polarization. Tests performed on the reflective bands of the NS001 thematic mapper simulator, an aircraft multispectral scanner, show that it is very sensitive to the polarization state of the incoming radiations. For 100% linearly polarized light, errors in the measured intensity vary from −40 to +40%, depending on the scan angle and spectral band. To estimate polarization-induced errors in the intensity measured at aircraft level, the intensity and polarization of the atmospheric radiances were simulated using a realistic Earth-atmosphere radiative transfer model. For the polarization of atmospheric radiances in the solar meridian plane over a vegetated target, intensity errors may range from −10 to +10%. The polarization-induced errors are highest in the shortest NS001 spectral band (0.450–0.525 μm) because of large atmospheric polarizations contributed by Rayleigh particles and small diluting effects caused by the small contributions of weakly polarized radiations coming from aerosols and the surface. Depending on the illumination and view angles, the errors in derived surface reflectance due to the radiance errors can be very large. In particular, for large off-nadir view angles in the forward scattered direction when the Sun is low, the relative errors in the derived surface reflectance can be as large as 4 to 5 times the relative error in the radiances. Polarization sensitivity errors cannot be neglected for the shorter wavelengths when the surface reflectance contribution to atmospheric radiances is very small.

Radiometric calibration of an airborne multispectral scanner

The absolute radiometric calibration of the NS001 Thematic Mapper Simulator reflective channels was examined based on laboratory tests and in-flight comparisons to ground measurements. The NS001 data are calibrated in-flight by reference to the NS001 internal integrating sphere source. This sources power supply or monitoring circuitry exhibited greater instability in-flight during 1988-1989 than in the laboratory. Extrapolating laboratory behavior to in-flight data resulted in 7-20 percent radiance errors relative to ground measurements and atmospheric modeling. Assuming constancy in the sources output between laboraotry and in-flight resulted in generally smaller errors. Upgrades to the sources power supply and monitoring circuitry in 1990 improved its in-flight stability, though in-flight ground reflectance based calibration tests have not yet been performed.

EOS Aura atmospheric chemistry data products

The Aura satellite (launch July, 2004) contains four instruments (http://aura.usfc. nasa.gov/) for studying the chemistry and dynamics of the atmosphere. The instruments include the High-Resolution Dynamics Limb Sounder (HIRDLS), Microwave Limb Sounder (MLS), the Ozone Monitoring Instrument (OMI), and the Tropospheric Emission Spectrometer (TES). This presentation discusses the Aura standard data products. Tools for accessing, reading, visualization and analysis of these data are also presented

Highlights of MODIS products

A new collection of Earth science data is now publicly available for the understanding of the land, ocean, and atmospheric interactions and how they affect our climate system. Approximately 40 higher level science standard products are being produced from the Moderate Resolution Imaging Spectroradiometer (MODIS) high resolution radiances. MODIS data starting November 1, 2000 to the present have been processed with an improved calibration algorithm (version-3) and data products are available to the public and science user community. Nearly all of these products have been evaluated and found useful for science and various applications. Radiometric calibrated and geolocated radiance data and all derived atmospheric, land and ocean products are available free from NASAs Distributed Active Archive Centers (DAACs).

In-Flight Radiometry of an Airborne Multispectral Sensor

The in-flight radiometric behavior of the NS001 Landsat Thematic Mapper simulator is being reexamined. The absolute radiometric calibration and polarization sensitivity are being analyzed based on data collected in 1990 and 1991. The NS001 has continuously variable gain settings controlled by the aircraft operator. As such, the of in-flight calibration source, an integrating sphere in the solar reflective spectrum, is the only means for calibrating this instrument. Upgrades to the power supply and monitoring circuitry in 1990 improved the in-flight stability. Preliminary results in-flight calibrations of the NS001 indicate no improvement in radiometric accuracy. Laboratory tests have also shown that the NS001 shows strong sensitivity to the degree of polarization and state of the incoming radiations. Simulation studies for typical in-flight conditions have shown that for the NS001 scanning in the principal plane of the sun over a vegetated target, radiance errors reached +/-10 percent in the 0.45-0.52-micron channel and varied with scan angle.

Goddard Atmospheric Composition Data Center: Aura data and services in one place

The Goddard Atmospheric Composition Data and Information Services Center (AC-DISC) is a portal to the atmospheric composition specific, user driven, multi-sensor, on-line, easy access archive and distribution system employing data analysis and visualization, data mining, and other user requested techniques for the better science data usage. It provides convenient access to atmospheric composition data and information from various remote-sensing missions, from TOMS, UARS, MODIS, and AIRS, to the most recent data from Aura OMI, MLS, HIRDLS (once these datasets are released to the public), as well as atmospheric composition datasets residing at other remote archive sites.

Atmospheric products from the Upper Atmosphere Research Satellite (UARS)

Abstract The Upper Atmosphere Research Satellite (UARS) was the first satellite to be launched under the Earth Observing System (EOS) science program of multi-mission observing systems of the National Aeronautics and Space Administrations (NASA). The EOS program was conceived to advance the understanding of the Earth-Atmosphere system on the global scale. The UARS was launched in September 1991 with ten instruments dedicated entirely to increase the understanding of chemistry and dynamics of the Earths stratosphere and mesosphere. After 10 years of successful data collection (far exceeding the originally projected lifetime of 3 years), the official mission ended in September 2001. However, seven instruments aboard UARS are still operational and six regularly take measurements. It is expected that the UARS will overlap the Earth Observing System (EOS) Aura satellite (to be launched in early 2004) for several months before the end of the UARS mission. The UARS data and atmospheric chemistry and dynamics data from other satellites are archived at the NASA Goddard Earth Sciences Distributed Active Archive Center (GES DAAC) and are available free to the public and science user community. The UARS data and related documents may be accessed through the GES DAAC website (http://daac.gsfc.nasa.gov). This paper gives an overview of the UARS data products. Detailed information on UARS instruments, mission highlights and related publications are available from the UARS project website (http://umpgal.gsfc.nasa.gov)