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Branch personnel are associated with upcoming space flight projects as science team members, principal investigators or
project scientists. This project-related research is often the culmination of long-term analysis of aircraft data and numerical
model results. This section describes the space flight projects in which there is significant Branch involvement.
The Tropical Rainfall Measuring Mission (TRMM)
Significant portions of the Branch's activities relate to the Tropical Rainfall Measuring Mission (TRMM). The main goal
of TRMM is to better understand the global energy and water cycles by providing distributions of rainfall and inferred heating
over the entire tropics. TRMM will help us understand the mechanisms by which tropical rainfall and its variability influence
global circulation. It will improve our ability to model these processes, with the ultimate goal being the prediction of global
circulation and rainfall variability at monthly and longer time scales. Branch TRMM research is focused on development and
application of algorithms to derive precipitation information from TRMM, numerical modeling of tropical rainfall systems and
the use of aircraft data for the validation of TRMM results.
TRMM is a U.S./Japan joint space project, with several other nations contributing to the science and validation
programs. The satellite, Figure 21, will be launched by the Japanese H2 rocket in late 1997, with a planned three-year
lifetime. The rain package consists of three instruments: 1) a 14 GHz rain radar with 4 km horizontal and 250 m vertical
resolution; 2) a multichannel dual-polarized passive microwave radiometer with frequencies between 10 and 86 GHz; and 3) a
five-channel visible/infrared instrument. The orbit elevation has been chosen as 350 km to obtain high resolution. The surface
swath is 220 km for the radar and 600 km for the other instruments. In order to document the diurnal rain variability, the orbit is
inclined at 35o so that the overpasses occur at different local times on successive days.
Rainfall data sets over the global tropics and the associated release of latent heat are needed to improve climate models,
which presently parameterize precipitation processes rather crudely. The large spatial and temporal variations in tropical rain
make it particularly difficult to measure from the Earth's surface. The problem is most acute over oceans, where present
observational information is uncertain and the differences among the leading global models are large. Adequate measurement of
rainfall over the global tropics can only be made from space, and TRMM, using an inclined low orbit and a combination of
sensors, will provide the most accurate estimation of tropical precipitation ever made.
In addition to the instruments focusing on precipitation a CERES (Clouds and the Earth's Radiant Energy System)
instrument was added to the TRMM payload to measure the Earth's radiation budget. This instrument will permit TRMM to
determine the radiative properties of the same cloud systems for which rain and latent heat release are being evaluated. Cloud
radiation is probably, together with rain, one of the main atmospheric variables for which information is badly needed to
improve the reliability of climate models. Also, a Lightning Imaging Sensor (LIS) was added to the instrument complement. It
will allow for the derivation of a lightning climatology over the tropics and the relating of lightning observations to the rainfall
distribution in tropical systems.
Geoscience Laser Altimeter System (GLAS)/Earth Observing System (EOS)
Scheduled for launch in 2002 as part of NASA's Earth Observing System (EOS), the Geoscience Laser Altimeter
System (GLAS) will provide continuous laser sounding of the earth's atmosphere from space for the first time. From its polar
orbit about 700 km above the surface, GLAS will employ a 40 Hz solid state laser operating at 1064 and 532 nm to measure
topography to an accuracy of 10 cm. Simultaneously, the atmospheric channels (1064 and 532 nm) of GLAS will provide
profiles of atmospheric backscatter from 40 km to the ground with 75 meter vertical resolution. These measurements will give
scientists an unprecedented global data set on the vertical structure of clouds and aerosols. This will greatly aid research efforts
aimed at understanding the effects of clouds and aerosols on climate and their role in climate change. To better understand and
predict the performance of the GLAS atmospheric channels, a computer model was developed to simulate the type of signal
that the instrument would likely produce. Such a model is necessary for determining the design requirements of the sensor and
for ascertaining the resolutions with which various atmospheric measurements can be obtained for a given configuration.
 Figure 22
shows the results of a nighttime simulation for expected GLAS results. The highest signal is white and decreases through the
brown, purple, green and blue tones. The lowest signal is dark blue. The results clearly show that GLAS will be capable of
measuring thin cirrus and boundary layer height at horizontal resolutions of a few kilometers and denser clouds at sub-kilometer
scales.
The Infrared Spectral Imaging Radiometer (ISIR) is a small, low-cost multispectral infrared instrument flown as a Space
Shuttle Hitchhiker payload. ISIR obtains radiometrically calibrated infrared imagery of cloud tops to advance observations of
cloud radiative properties. ISIR Tests new IR Imaging Technology: (1) an advanced warm area (uncooled) silicon
microbolometer array detector, eliminating the need for cryogenic cooling; (2) a pushbroom scanning technique, eliminating the
requirement for mechanical scanning systems; and (3) time delay integration (TDI), improving radiometric precision by the
square root of the along-track detector elements. Spectral imagery is obtained in three narrow infrared bands with a resolution
of 250 meters and a swath width of 80 km. An artist's conception of the ISIR in orbit is shown in Figure 23. In 1997 ISIR will
fly on STS-85 in combination with the Shuttle Laser Altimeter Lidar to provide a test of combined lidar and IR radiometer
observations from space.
Polarization and Directionality of The Earth's Reflectances (POLDER)
The POLDER (Polarization and Directionality of the Earth's Reflectances) instrument will observe from space the
polarization, directional, and spectral characteristics of reflected solar light by the earth-atmosphere system. Developed by
Centre National d'Etudes Spatiales (CNES) of France, POLDER is scheduled to be launched in the fall of 1996 onboard the
Japanese Advanced Earth Observing Satellite (ADEOS). The participation by the Mesoscale Atmospheric Processes Branch
at GSFC with the POLDER instrument is based on the similarity and cooperative nature of our ongoing aircraft remote sensing
work. In particular, the Tilt Scan CCD Camera (TSCC) was developed for bi-directional reflectance distribution function
(BDRF) measurements of clouds and other scenes, and also acquires polarization imagery. The TSCC instrument is scheduled
to provide validation of POLDER measurements of cloud reflectances by matching POLDER satellite overpasses with
underflights using the ER-2 TSCC for BDRF and degree of polarization comparisons. A comparison of the instruments will
investigate the extrapolation of observations of cloud BDRF that are high resolution but of limited coverage (TSCC), to data
that are coarse spatial resolution but with global coverage (POLDER).
Advanced Microwave Scanning Radiometer (AMSR)/Earth Observing System (EOS)
The Advanced Microwave Scanning Radiometer (AMSR) is a Japanese instrument designed to observe atmospheric
water vapor, cloud liquid water, precipitation, sea surface temperature, sea ice and ocean surface wind speed using frequencies
from 6 to 90 GHz. The AMSR will fly on both the Japanese ADEOS-II satellite to be launched in 1999 and on the EOS-PM
satellite in 2000. The AMSR, with its larger antenna providing increased spatial resolution and with its additional low-frequency
channels, will provide the basis for significantly improved precipitation estimates compared to currently available
instrumentation. Vertical hydrometeor structure and the vertical profile of heating will also be derived using AMSR data. The
AMSR, in combination with TRMM, will provide new insight into global precipitation patterns.
The Geosynchronous Operational Environmental Satellites (GOES) provide the nation with several useful services, most notably with animated images of the clouds-in-motion which are vital to detecting outbreaks of severe weather. NASA-GSFC provides the project engineering and scientific expertise to NOAA/NESDIS for construction and launch of the GOES weather satellites. In turn, NASA scientists frequently use the GOES visible and infrared radiometers to study the dynamics of storms, winds, clouds, precipitation and surface conditions at high resolution, particularly to "set the scene" during field campaigns. In addition, GOES observations are used by climate analysts to determine the diurnal variability of temperature, moisture, clouds and rainfall in the western hemisphere. In the future, more advanced GOES instruments are being planned that will be able to continuously monitor mesoscale atmospheric processes to supplement the scientific analyses from rest of the earth observing system.
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Figure 22
shows the results of a nighttime simulation for expected GLAS results. The highest signal is white and decreases through the
brown, purple, green and blue tones. The lowest signal is dark blue. The results clearly show that GLAS will be capable of
measuring thin cirrus and boundary layer height at horizontal resolutions of a few kilometers and denser clouds at sub-kilometer
scales.
The Geosynchronous Operational Environmental Satellites (GOES) provide the nation with several useful services, most notably with animated images of the clouds-in-motion which are vital to detecting outbreaks of severe weather. NASA-GSFC provides the project engineering and scientific expertise to NOAA/NESDIS for construction and launch of the GOES weather satellites. In turn, NASA scientists frequently use the GOES visible and infrared radiometers to study the dynamics of storms, winds, clouds, precipitation and surface conditions at high resolution, particularly to "set the scene" during field campaigns. In addition, GOES observations are used by climate analysts to determine the diurnal variability of temperature, moisture, clouds and rainfall in the western hemisphere. In the future, more advanced GOES instruments are being planned that will be able to continuously monitor mesoscale atmospheric processes to supplement the scientific analyses from rest of the earth observing system.