William J. Wilson

Development of a high stability L-band radiometer for ocean salinity measurements

An NEDT analysis of a Dicke radiometer with noise diode injection is presented. The analysis is formulated for a calibration that would form separate running averages of receiver noise temperature and of gain in order to minimize the NEDT and maximize the antenna observation duty cycle relative to the reference and noise diode duty cycles. Results are applied to the Aquarius ocean salinity radiometer problem to show that near ideal total-power radiometer performance is possible.

Millimeter-Wave Imaging Sensor

A scanning 3-mm radiometer system has been built and used on a helicopter to produce moderate resolution (0.5°) images of the ground. This mm-wave sensor can be used for a variety of remote sensing applications, and produces images through clouds, smoke, and dust when visual and IR sensors are not usable. The system is described, and imaging results are presented.

A Broad-Band Low-Noise 205 GHz Radiometer for a Satellite Receiver

A low-noise room temperature 205 GHz heterodyne radiometer has been designed and built for the Upper Atmosphere Research Satellite Microwave Limb Sounder instrument. The radiometer design features a low loss quasi-optical broad-band signal/LO coupler, a solid state local oscillator and a single-ended fundamental mixer.

GeoSTAR: a synthetic aperture microwave sounder for geostationary missions

The Geostationary Synthetic Thinned Aperture Radiometer (GeoSTAR) is a new microwave atmospheric sounder under development. It will bring capabilities similar to those now available on low-earth orbiting environmental satellites to geostationary orbit - where such capabilities have not been available. GeoSTAR will synthesize the multi-meter aperture needed to achieve the required spatial resolution, which will overcome the obstacle that has prevented a GEO microwave sounder from being implemented until now. The synthetic aperture approach has until recently not been feasible, due to the high power needed to operate the on-board high-speed massively parallel processing system required for 2D-synthesis, as well as a number of system and calibration obstacles. The development effort under way at JPL, with important contributions from the Goddard Space Flight Center and the University of Michigan, is intended to demonstrate the measurement concept and retire much of the technology risk. To that purpose a small ground based demo version of GeoSTAR is being constructed, which will be used to characterize system performance and test various calibration methods. This prototype development, which is being sponsored by NASA through its Instrument Incubator Program, will be completed in 2005. A GeoSTAR space mission can then be initiated. In parallel with the technology development, mission architecture studies are also under way in collaboration with the NOAA Office of System Development. In particular, the feasibility of incorporating GeoSTAR on the next generation of the geostationary weather satellites, GOES-R, is being closely examined. That would fill a long standing gap in the national weather monitoring capabilities.

Millimeter-wave Array Receivers for Remote Sensing

Recent developments in millimeter-wave receiver have enabled new remote sensing capabilities. MMIC circuits operating at frequencies as high as 200 GHz have enabled low-cost mass producible integrated receivers suitable for array applications. We will describe several ground-based demonstrations of this technology including development of integrated spectral line receivers for atmospheric remote sensing, a synthetic thinned aperture radiometer for atmospheric sounding and imaging and polarimetric array radiometers for astrophysics applications.

Development of a high stability L-band radiometer for the Aquarius ocean salinity mission

The NASA Earth Science System Pathfinder (ESSP) mission Aquarius, will measure global ocean surface salinity with ~100 km spatial resolution every 7-days with an average monthly salinity accuracy of 0.2 psu (parts per thousand). This requires an L-band low-noise radiometer with the long-term calibration stability of less than or equal to 0.1 K over 7 days. A three-year research program on radiometer stability has addressed the radiometer requirements and configuration necessary to achieve this objective. The system configuration and component performance have been evaluated with radiometer test beds at both JPL and GSFC. The research has addressed several areas including component characterization as a function of temperature, system linearity, noise diode calibration, temperature control of components and optimum switching of the Dicke switch for lowest noise performance. A breadboard radiometer, utilizing microstrip-based technologies, has been built to demonstrate this long-term stability. This paper will present the results of the radiometer test program and details on the design of the Aquarius radiometer. The operational sequence that will be used to achieve the low noise and stability requirements will also be discussed.

Design of a geostationary microwave precipitation radiometer

The Geostationary Microwave Precipitation Radiometer will be a passive microwave radiometer system to be flown on the NASA Geostationary Earth Observatory. This instrument will provide microwave images for meteorology. It will measure radiation from the Earth and its atmosphere in seven frequency bands from 37 to 220 GHz. The instrument will have a 4 m Cassegrain antenna which will be mechanically scanned to provide images of the Earth in approximately equals 2 hours.

Synthetic aperture imaging radiometer

A concept for a high spatial resolution passive microwave instrument is presented. In a low Earth orbit, the Synthetic Aperture Imaging Radiometer (SAIR) instrument would provide microwave images with a 5 km spatial resolution, that is 10 times better than current spaceborne passive microwave sensors. The scientific applications would be for high spatial resolution measurements of sea and land ice, snow cover, and rainfall. The SAIR would be a low cost, low mass, non-scanning instrument that could be launched with a small launch vehicle.

The NGC 7538 region - The distribution and dynamics of molecules compared with those of HI and H/+/

CO maps and preliminary H2S and H2CO data for the molecular cloud associated with the HII region NGC 7538 are compared with the distributions of ionized and neutral hydrogen. South of the optical HII region is a ridge of high 13CO column density with cold, self-absorbed HI gas just beyond it. A dense clump within the ridge is found adjacent to the HII region in the southeast. The percentage of the hydrogen in atomic form varies from - 0.1% in the dense region to - 0.8% in the outskirts. The lower-density region of expanding gas seen next to the HII region in the southwest is attributed to the passage of a molecular dissociation wave.