The Iridium communications satellite constellation is a swarm of 66 LEO satellites in 6 pole-crossing orbits. Iridium
LLC plans a NEXT generation to be launched 2013-16, and has invited secondary "bolt and go" payloads from Earthobserving
agencies. A swarm of infrared imagers on Iridium-NEXT could track water vapor and clouds to estimate the
unobserved winds above the 55-60 degree latitude limit of geosynchronous satellite imagery. This kind of polar overpass
data has been demonstrated to significantly improve medium-range weather forecasts by tracking water vapor features at
6.7 microns in successive images near the pole from NASA's MODIS instruments. A "Boreas" instrument design is
proposed for a push-broom imager combining two miniature sensors: uncooled microbolometric cameras gathering 4-
band infrared radiometry, and small star trackers providing attitude information. An autonomous instrument package
has been designed with low mass, power, and data rate. The "Boreas" instrument would use the Iridium constellation
itself to relay the raw imagery from 3 successive images to ground stations that would navigate the data and extract wind
vectors. Wind vectors could be generated automatically for the polar caps every few hours, and delivered for
assimilation into numerical weather models during Iridium-NEXT operations, during 2016-2030.
During 1997-98, the NASA-NOAA Advanced Geosynchronous Studies (AGS) program sponsored work to explore the possibility of designing a high-quality imaging radiometer for the future GOES platforms. The AGS Imager (AGSI) design calls for the acquisition of 12-bit digital images every few minutes in 18 spectral bands with horizontal resolutions ranging from 0.3 to 1.5 km on a full-earth disk. The resulting raw sensor data stream is approximately 300 Mbits/sec, uncompressed. The AGSI ground system must convert the sensor data into calibrated, earth-located 'Level 1b' images and deliver them to NOAA and to the science community within minutes of reception. To accomplish this high-speed digital-image delivery, the AGSI downlink design calls for lossless compression to 150 Mbits/sec, packetized using CCSDS standards with error-correction, and broadcast in Ka- band to a low-precipitation site like White Sands, NM.
Desktop computers have evolved to the point where they can process GOES variable-length (GVAR) data blocks at 1 Gbyte/hour, despite the complexity of the data stream and the varied demands of realtime users. Because of the lack of off-the-shelf GVAR processing packages before the launch of GOES-I in 1994, we assembled a custom open system at NASA- GSFC to automatically ingest, process and disseminate full- resolution GOES-8 and GOES-9 imagery 24 hours per day. This data service is now widely used by the internet community. The hardware-software package described here can be copied freely. Similar systems are now available from commercial vendors.
By using current technology, it appears possible to build and launch a prototype for an advanced geosynchronous imager on a small within a few years. This could be done independently of upgrading the other GOES mission functions of atmospheric sounding, communications, and space- and solar-monitoring. At NASA-GSFC, we are engaged in a feasibility study for a Geosynchronous Advanced Technology Environmental System (GATES). GATES is envisioned as a high performance imager on a small dedicated satellite with a complete ground system. GATES could fly in the era of the Earth Observing System and serve as a prototype for NOAA's next generation of operational satellites. In addition to carrying all the channels identified for NOAA's GOES-R Imager, GATES is being designed to carry all the broadband channels specified for NASA's Moderate-resolution Imaging Spectro-radiometer instrument on the EOS platforms. This channel complement gives GATES the capability to fill in the space-time gaps in cloud observations from polar-orbiting satellites and to serve as a cross-reference between polar radiometers. Multispectral rapid-imaging requirements are met by using several recently developed technologies: large detector arrays with active cooling, star-tracking and gyroscopic attitude-determination, a small and rigid spacecraft, a heat-resistent telescope, a phased-array Ka- band downlink, realtime digital image rectification, and Internet data distribution on the ground. The GATES design is so small and agile that it could use the momentum wheels to scan the entire spacecraft back-and-forth across the Earth.
Marine statiform clouds (MSC) cover large areas of the globe that are visible to GOES. The operational satellite cloud retrieval algorithms are prone to biases when analyzing MSC, due to the often sub-pixel size cloud elements and radiative temperatures close to that of the underlying ocean. For example, the relatively large pixel size and calibration drifts in GOES-7 imagery have made it difficult to extract unbiased MSC properties using thermal threshold techniques. Here, we apply a novel retrieval approach to the two important MSC regimes which can be monitored well from the GOES-8 satellite: the Pacific Ocean just west of California/Baja and Peru/Chile. MSC cloud parameters for these areas are retrieved together with surface temperature and column water vapor in a temporally and spatially consistent manner that is insensitive to sensor resolution and calibration errors. Semi-operational analysis of GOES-8 imagery began in December 1995. So, the main focus is on assessing the diurnal variability of MSC. Following a brief description of the retrieval technique, we present initial results describing the full diurnal cycle of MSC fractional cloud cover and cloud top temperature, monitored using the single-channel version of the algorithm. In addition, we address the daytime variability of other important cloud parameters using a bispectral extension of the retrieval scheme. The results are also compared with other pertinent MSC analyses.
The new generation of Geostationary Operational Environmental Satellites (GOES) have an imager instrument with five multispectral bands of high spatial resolution,and very high dynamic range radiance measurements with 10-bit precision. A wide variety of environmental processes can be observed at unprecedented time scales using the new imager instrument. Quality assurance and feedback to the GOES project office is performed using rapid animation at high magnification, examining differences between successive frames, and applying radiometric and geometric correction algorithms. Missing or corrupted scanline data occur unpredictably due to noise in the ground based receiving system. Smooth high resolution noise-free animations can be recovered using automatic techniques even from scanline scratches affecting more than 25 percent of the dataset. Radiometric correction using the local solar zenith angle was applied to the visible channel to compensate for time- of-day illumination variations to produce gain-compensated movies that appear well-lit from dawn to dusk and extend the interval of useful image observations by more than two hours. A time series of brightness histograms displays some subtle quality control problems in the GOES channels related to rebinning of the radiance measurements. The human visual system is sensitive to only about half of the measured 10- bit dynamic range in intensity variations, at a given point in a monochrome image. In order to effectively use the additional bits of precision and handle the high data rate, new enhancement techniques and visualization tools were developed. We have implemented interactive image enhancement techniques to selectively emphasize different subranges of the 10-bits of intensity levels. Improving navigational accuracy using registration techniques and geometric correction of scanline interleaving errors is a more difficult problem that is currently being investigated.
Geostationary orbit provides a wonderful viewpoint for collecting movies of meteorological processes. Because GOES- 8 images are large and frequent, high-performance workstations and user-friendly software are required to review the current pools of GOES weather imagery at full resolution. During the post-launch checkouts, the GOES-8 and GOES-9 satellites were exercised in rapid-scan imaging modes that challenge most display systems. At NASA-GSFC, the Interactive Imaging Spread Sheet (IISS) software/hardware was used to roan and zoom through gigabytes of GOES image data collected in 1994-95. We use the IISS to examine exciting meteorological features within the hurricanes of 1995 and during typical episodes of severe weather that occur somewhere over the United States every day. The IISS demonstration shows how weather forecaster could make good use of the full resolution and depth of GOES-8 imagery, adapting to the meteorological even as it develops, especially when synchronized with corresponding weather radar.