Hans-Juergen C. Blume

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.

The effect of monomolecular surface films on the microwave brightness temperature of the sea surface

Abstract Airborne microwave radiometer measurements at 1·43 and 2·65 GHz over a sea surface covered with a monomolecular oleyl alcohol surface film and over adjacent slick sea surfaces are presented. The measurements show that at 2·65 GHz the brightness temperature T B is not affected by the slick, while at 1·43 GHz it drops from 93 K to a minimum value of almost O K. This implies that at 1·43 GHz the emissivity of the slick-covered sea surface is extremely small, similar to a metallic layer, and that this resonant-type phenomenon is confined to a narrow frequency band of width δƒ/ ƒ<0·6. The theoretical implications of these experimental findings are discussed in the framework of the Debye relaxation theory of polar liquids. It is conjectured that a thin layer of water molecules polarized by the surface film gives rise to an anomalous dispersion, which causes the large decrease in brightness temperature at 1·43 GHz. The modulus of the relative dielectric constant e∗ is estimated to be ≥ 5·2 × 10−4 and th...

Radiometric observations of sea temperature at 2.65 GHz over the Chesapeake Bay

The present work describes the various corrections necessary in order to deduce ocean surface temperature from S -band microwave radiometer measurements and applies these results to a series of data obtained with a high absolute accuracy radiometer. Measurements made with a 2.65 GHz radiometer from an aircraft flown over the Chesapeake Bay area are presented and compared in detail with accurately obtained sea truth data. For the calm sea, it was found that the observed brightness temperature agreed well with that calculated from the known sea surface and atmospheric properties over a fairly wide range of surface salinity values (0.2 per mille to 25 per mille). For cases where the surface wind speeds are of the order of 7 to 15 knots, an excess brightness temperature was observed which is attributable to surface roughness and microscale surface disturbances. The excess brightness temperature dependence on wind speed was found to correlate to a certain extent with the rms wave slope dependence on wind speed.

Variation of the Microwave Brightness Temperature of Sea Surfaces Covered with Mineral And Monomolecular Oil Films

Airborne microwave radiometer measurements over mineral and monomolecular oil films and adjacent clean sea surfaces are reported. An artificial crude-oil spill experiment in the New York Bight area showed a brightness temperature increase of the sea surface at 1.43 GHz as expected from a multilayered system with different dielectric constants. However, a monomolecular surface-film experiment with oleyl alcohol conducted in the North Sea during MARSEN in 1979 showed a strong brightness temperature depression at 1.43 GHz and no change in brightness temperature at 2.65 GHz. It is postulated that the monomolecular layer, because of its physical and chemical properties, polarized the underlying water molecules so strongly that the emissivity decreased from 0.31 to 0.016. It is estimated that the effective dielectric constant changed from 90 to 5.2 × 104. Because these phenomena occurred at 1.43 GHz it may be concluded that this frequency is very close to the center of a new anomalous dispersion region resulting from a restructuring of the water layer below the surface film.

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.

Radiometric observations of sea temperature at 2.65 GHZ over the chesapeake bay

The present work describes the various corrections necessary in order to deduce ocean surface temperature from S -band microwave radiometer measurements and applies these results to a series of data obtained with a high absolute accuracy radiometer. Measurements made with a 2.65 GHz radiometer from an aircraft flown over the Chesapeake Bay area are presented and compared in detail with accurately obtained sea truth data. For the calm sea, it was found that the observed brightness temperature agreed well with that calculated from the known sea surface and atmospheric properties over a fairly wide range of surface salinity values (0.2 per mille to 25 per mille). For cases where the surface wind speeds are of the order of 7 to 15 knots, an excess brightness temperature was observed which is attributable to surface roughness and microscale surface disturbances. The excess brightness temperature dependence on wind speed was found to correlate to a certain extent with the rms wave slope dependence on wind speed.

Passive microwave detection of river-plume fronts in the German Bight

Abstract The location of oceanic fronts became important to the ocean community because sonar transmissions were distorted and disrupted at those locations. The oceanic fronts, including shelf-sea and river-plume fronts, are locations of higher than normal horizontal temperature and/or salinity gradients in ocean waters. For the detection of oceanic fronts, the Maritime Remote Sensing Experiment (MARSEN) programme included the NASA L- and S-band radiometer system on board the NASA P-3 aircraft from 30 August to 23 September 1979. The surface temperature and salinity measurements were concentrated to the freshwater outflows of the river Weser and Elbe in the German Bight. Three missions were conducted: 19, 22 and 23 September 1979. The values of salinity were plotted as a function of geographic position and contour maps of the salinity distribution were generated from the value plots. On 22 September 1979 during a noon flood-tide, two river-plume salinity fronts were detected when a body of water with high...

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.