Development of UHF radiometer

A wideband multifrequency UHF radiometer was initially developed to operate in the 500 to 710 MHz frequency range for the remote measurement of ocean water salinity. However, radio-frequency interference required a reconfiguration to operate in the single-frequency radio astronomy band of 608 to 614 MHz. Details of the radiometer development and testing are described. Flight testing over variable terrain provided a performance comparison of the UHF radiometer with an L-band radiometer for remote sensing of geophysical parameters. Although theoretically more sensitive, the UHF radiometer was found to be less desirable in practice than the L-band radiometer

Passive microwave mapping of ice thickness

Basic calculations are presented for evaluating the feasibility of a scanning microwave radiometer system for mapping the thickness of lake ice. An analytical model for the apparent brightness temperature as a function of ice thickness has been developed, and elaborated to include such variables as galactic and atmospheric noise, aspect angle, polarization, temperature gradient in the ice, the presence of transition layers such as snow, slush, and water, increased loss due to air inclusions in the ice layer, and the presence of multiple ice thicknesses within the antenna footprint. It was found that brightness temperature measurements at six or seven frequencies in the range of 0.4 to 0.7 GHz were required to obtain unambiquous thickness estimates. A number of data processing methods were examined. The effects of antenna beamwidth, scanning rate, receiver bandwidth, noise figure, and integration time were studied

Spaceborne sensors (1983-2000 AD): A forecast of technology

A technical review and forecast of space technology as it applies to spaceborne sensors for future NASA missions is presented. A format for categorization of sensor systems covering the entire electromagnetic spectrum, including particles and fields is developed. Major generic sensor systems are related to their subsystems, components, and to basic research and development. General supporting technologies such as cryogenics, optical design, and data processing electronics are addressed where appropriate. The dependence of many classes of instruments on common components, basic R&D and support technologies is also illustrated. A forecast of important system designs and instrument and component performance parameters is provided for the 1983-2000 AD time frame. Some insight into the scientific and applications capabilities and goals of the sensor systems is also given

THz Instruments for Space

Terahertz technology has been driven largely by applications in astronomy and space science. For more than three decades cosmochemists, molecular spectroscopists, astrophysicists, and Earth and planetary scientists have used submillimeter-wave or terahertz sensors to identify, catalog and map lightweight gases, atoms and molecules in Earth and planetary atmospheres, in regions of interstellar dust and star formation, and in new and old galaxies, back to the earliest days of the universe, from both ground based and more recently, orbital platforms. The past ten years have witnessed the launch and successful deployment of three satellite instruments with spectral line heterodyne receivers above 300 GHz (SWAS, Odin, and MIRO) and a fourth platform, Aura MLS, that reaches to 2520 GHz, crossing the terahertz threshold from the microwave side for the first time. The former Soviet Union launched the first bolometric detectors for the submillimeter way back in 1974 and operated the first space based submillimeter wave telescope on the Salyut 6 station for four months in 1978. In addition, continuum, Fourier transform and spectrophotometer instruments on IRAS, ISO, COBE, the recent Spitzer Space Telescope and Japan's Akari satellite have all encroached into the submillimeter from the infrared using direct detection bolometers or photoconductors. At least two more major satellites carrying submillimeter wave instruments are nearing completion, Herschel and Planck, and many more are on the drawing boards in international and national space organizations such as NASA, ESA, DLR, CNES, and JAXA. This paper reviews some of the programs that have been proposed, completed and are still envisioned for space applications in the submillimeter and terahertz spectral range

Resident research associateships. Postdoctoral and senior research awards: Opportunities for research at the Jet Propulsion Laboratory

Opportunities for research as part of NASA-sponsored programs at the JPL cover: Earth and space sciences; systems; telecommunications science and engineering; control and energy conversion; applied mechanics; information systems; and observational systems. General information on applying for an award for tenure as a guest investigator, conditions, of the award, and details of the application procedure are provided

Technical approaches, chapter 3, part E

Radar altimeters, scatterometers, and imaging radar are described in terms of their functions, future developments, constraints, and applications

Tour of the Electromagnetic Spectrum Booklet

This booklet introduces electromagnetic waves, their behaviors, and how scientists visualize these data. Each region of the spectrum is described and illustrated with examples of NASA science. It is a companion piece to the video series under the same title. Educational levels: Informal education

Aquarius and Remote Sensing of Sea Surface Salinity from Space

Aquarius is an L-band radiometer and scatterometer instrument combination designed to map the salinity field at the surface of the ocean from space. The instrument is designed to provide global salinity maps on a monthly basis with a spatial resolution of 150 km and an accuracy of 0.2 psu. The science objective is to monitor the seasonal and interannual variation of the large scale features of the surface salinity field in the open ocean. This data will promote understanding of ocean circulation and its role in the global water cycle and climate

Microwave Radiometry at Frequencies From 500 to 1400 MHz: An Emerging Technology for Earth Observations

icrowave radiometry has provided valuable spaceborne observations of Earth’s geophysical properties for decades. The recent SMOS, Aquarius, and SMAP satellites have demonstrated the value of measurements at 1400 MHz for observ- ing surface soil moisture, sea surface salinity, sea ice thickness, soil freeze/thaw state, and other geophysical variables. However, the information obtained is limited by penetration through the subsur- face at 1400 MHz and by a reduced sensitivity to surface salinity in cold or wind-roughened waters. Recent airborne experiments have shown the potential of brightness temperature measurements from 500–1400 MHz to address these limitations by enabling sensing of soil moisture and sea ice thickness to greater depths, sensing of temperature deep within ice sheets, improved sensing of sea salinity in cold waters, and enhanced sensitivity to soil moisture under veg- etation canopies. However, the absence of significant spectrum re- served for passive microwave measurements in the 500–1400 MHz band requires both an opportunistic sensing strategy and systems for reducing the impact of radio-frequency interference. Here, we summarize the potential advantages and applications of 500–1400 MHz microwave radiometry for Earth observation and review recent experiments and demonstrations of these concepts. We also describe the remaining questions and challenges to be addressed in advancing to future spaceborne operation of this technology along with recommendations for future research activities

Soil Moisture ActivePassive (SMAP) L-Band Microwave Radiometer Post-Launch Calibration

The SMAP microwave radiometer is a fully-polarimetric L-band radiometer flown on the SMAP satellite in a 6 AM/ 6 PM sun-synchronous orbit at 685 km altitude. Since April, 2015, the radiometer is under calibration and validation to assess the quality of the radiometer L1B data product. Calibration methods including the SMAP L1B TA2TB (from Antenna Temperature (TA) to the Earths surface Brightness Temperature (TB)) algorithm and TA forward models are outlined, and validation approaches to calibration stability/quality are described in this paper including future work. Results show that the current radiometer L1B data satisfies its requirements