Bruce M. Kendall

Measurement of ocean temperature and salinity via microwave radiometry

Sea-surface temperature with an accuracy of 1 °C and salinity with an accuracy of 1‰ were measured with a 1.43 and 2.65 GHz radiometer system after correcting for the influence of cosmic radiation, intervening atmosphere, sea-surface roughness, and antenna beamwidth. The radiometers are a third-generation system using null-balancing and feed-back noise injection. Flight measurements from aircraft over bay regions and coastal areas of the Atlantic resulted in contour maps with spatial resolution of 0.5 km.

Passive Microwave Measurements of Temperature And Salinity in Coastal Zones

A technique to remotely measure sea-surface temperature and salinity was demonstrated with a dual-frequency microwave radiometer system developed at the NASA Langley Research Center. Acuracies in temperature of 1°C and 1 part per thousand in salinity were obtained using state-of-the-art radiometers. Several aircraft programs for the measurement of coastal area waters demonstrating the application of the microwave radiometer system are discussed. Measurements of coastal zone ocean temperature and salinity are useful for studying the circulation in bay areas and tracing river outflow. Flight measurements in 1976 from an aircraft at an altitude of 1.4 km over the lower Chesapeake Bay and coastal areas of the Atlantic Ocean resulted in contour maps of sea-surface temperature and salinity with a spatial resolution of 0.5 km. Recent measurements (1980) at an altitude of 170 m were obtained over the Chesapeake Bay mouth and southward along the Virginia coast to study the Chesapeake Bay Plume. Because the surface area above submarine springs of fresh water exhibit temperatures and salinities lower than the surrounding sea waters, the multifrequency radiometer system was used in 1978 to detect submarine fresh water springs of the coastal areas around the island of Puerto Rico. Forty-four submarine fresh water springs were identified. In 1979, a quasi-synoptic survey of tidally induced salinity changes off the Georgia coast was performed using the microwave radiometers onboard a NASA aircraft.

Inflatable antenna microwave radiometer for soil moisture measurement

Microwave measurements of soil moisture are not being obtained at the required spatial Earth resolution with current technology. The Low Earth Orbit Microwave Radiometry Workshop held in Hampton, Virginia, identified measurements of soil moisture at a resolution of 10 km as the general science driver. Recently, new novel designs for lightweight reflector systems have been developed using deployable inflatable antenna structures which could enable lightweight real-aperture radiometers. In consideration of this, a study was conducted at the NASA Langley Research Center to determine the feasibility of developing a microwave radiometer system using inflatable reflector antenna technology to obtain high spatial resolution radiometric measurements of soil moisture from low Earth orbit and which could be used with a small and cost effective launch vehicle. The required high resolution with reasonable swath width coupled with the L-band measurement frequency for soil moisture dictated the use of a large (30 meter class) real aperture antenna in conjunction with a pushbroom antenna beam configuration and noise-injection type radiometer designs at 1.4 and 4.3 GHz to produce a 370 kilometer cross-track swath with a 10 kilometer resolution that could be packaged for launch with a Titan II class vehicle. This study includes design of the inflatable structure, control analysis, structural and thermal analysis, antenna and feed design, radiometer design, payload packaging, orbital analysis, and electromagnetic losses in the thin membrane inflatable materials.<<ETX>>

Microwave radiometer sensor technology research for Earth science measurements

A research program has been initiated at NASA Langley Research Center to investigate the critical technologies for developing advanced microwave radiometers suitable for Earth science observations. A significant objective of this research is to enable microwave measurements with adequate spatial resolutions for a number of Earth science parameters, such as sea ice, precipitation, soil moisture, sea surface temperature, and wind speed over oceans. High spatial resolution microwave sensing from space with reasonable swath widths and revisit times favor large real aperture radiometer systems. However, the size requirements for such systems are in conflict with the need to emphasize small launch vehicles. This paper describes a tradeoff between the science requirements, basic operational parameters, test configurations, and expected sensor performance for a satellite radiometer concept. The preliminary designs of real aperture systems utilizing novel light-weight compact-packaging techniques are used as a means of demonstrating this technology.

Submarine fresh water outflow detection with a dual-frequency microwave and an infrared radiometer system

The surface area above submarine springs of fresh water exhibit temperatures of 4°C and salinities of 5 °/oo lower than the surrounding sea waters. The Langley multifrequency radiometer system which earlier demonstrated (Blume et al, 1978) an accuracy of 0.3°C and 1 °/oo in remotely detecting the surface temperature and salinities respectively was used to detect submarine fresh water springs. The first mission on February 4, 1978 consisted of overflight measurements over 3/4 of the coastal areas around the island of Puerto Rico. During the second mission on February 6, 1978 special attention was directed to the northwest portion of Puerto Rico where several submarine springs had been reported.

Advanced systems requirements for ocean observations via microwave radiometers

A future microwave spectroradiometer operating in several frequency bands will have the capability to step or sweep frequencies on an adaptable or programmable basis. The on-board adaptable frequency shifting can make the systems immune from radio interference. Programmable frequency sweeping with on-board data inversion by high speed computers would provide for instantaneous synoptic measurements or sea surface temperature and salinity, water surface and volume pollution, ice thickness, ocean surface winds, snow depth, and soil moisture. Large structure satellites will allow an order of magnitude improvement in the present radiometric measurement spacial resolution.