Parametric calculations of the microwave emission from the ocean surface are presented to determine the optimum electromagnetic wavelength for measuring salinity. At 800 MHz, a target accuracy of 240 parts per million is within the state of the art provided that emission due to surface roughness is negligible, or correctable, and that the error resulting from galactic radiation can be removed using an upward-looking antenna. Examples of salinity measurements relevant to physical oceanography are presented, and a possible spacecraft University of Massachusetts, Amherst, MA 01003.system is discussed.

Considerations for Microwave Remote Sensing of Ocean-Surface Salinity

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.

Measurement of ocean temperature and salinity via microwave radiometry

This paper reviews the current status of passive microwave remote sensing of the ocean. The physics of emission and instrumentation are highlighted in order to establish a relationship between the thermal emission and retrieved geophysical parameters. A discussion then follows on measurements of temperature, salinity, windspeed, etc. using passive microwave systems. These measurements are related to the accuracy and spatial resolution required by the users. The status of passive microwave remote sensing is summarized and recommendations for future research are presented.

Passive microwave remote sensing of the ocean - A review

Preliminary design details and laboratory test results of a prototype microwave radiometer operating near 20 GHz are presented. Radiometric stability to 10 millikelvin on time scales from 100 to 10,000 s is the goal for the final system. The use of noise diodes as receiver gain calibrators is examined, and test results showing 30 parts per million stability per day in the intercomparison of noise diodes are presented. Temperature control of the radiometer is also examined, and the design of a solid state temperature control system capable of 1 mK stability near room temperature is presented. A new design for a mechanically actuated Dicke switch is also presented. The results of these laboratory developments are applied to a prototype radiometer. Early indications are that design goals are being met in the prototype. Future confirmation of the system's theoretical performance will only be possible with the completion of the final radiometer units.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97RS02749

Development of a High Stability Water Vapor Radiometer

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 14 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 05 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

Passive Microwave Measurements of Temperature And Salinity in Coastal Zones

A radiometer for the remote measurement of sea surface temperature is described. Two requirements are necessary for the attainment of an absolute accuracy of 1 or 2 K in molecular temperature. Although the first is inappropriate for discussion here, it is clear that corrections must be developed to account for perturbations caused by surface effects (roughness, foaming, and salinity changes) and for atmospheric effects (absorption and scattering). The second requirement, namely, the development of an instrument capable not only of high relative accuracy (i.e., resolution) but also of high absolute precision, is the subject of this paper. The concepts underlying the design of an instrument capable of an absolute accuracy of a few tenths degrees Kelvin in the measurement of brightness temperature at S band are described. The role of the antenna is discussed and the importance of high ohmic and beam efficiencies is stressed. The hardware itself is fully described, along with an outline on the design of a unique cryogenically cooled termination used to calibrate the whole radiometer, including antenna. Finally, some test results are presented that show that the design goals for the instrument have been closely approached.

K.W. Gray

Papers

An S-Band Radiometer Design with High Absolute Precision