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

Blume, Hans-Juergen C.; Love, A.; Melle, M. Van; Ho, W.J.

doi:10.1109/tap.1977.1141547

Cited by 24 publications

(5 citation statements)

References 15 publications

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“…[8] The computation of T b wind is derived from the twoscale electromagnetic model of Yueh [1997]; small sea waves (which induce Bragg scattering) are superimposed on large sea waves (which reflect electromagnetic waves as infinite planes). Results of this model agree with measurements performed at S-and L band by Hollinger [1971], Blume et al [1977] and Wilson et al [2001] that showed that wind induces noticeable increase in T b at low frequencies (a few tenths of a Kelvin per m s À1 ). A precise parameterization of the wind influence is crucial for SSS retrieval.…”

Section: Introductionsupporting

confidence: 88%

Issues concerning the sea emissivity modeling at L band for retrieving surface salinity

et al. 2003

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[1] In order to prepare the sea surface salinity (SSS) retrieval in the frame of the Soil Moisture and Ocean Salinity (SMOS) mission we conduct sensitivity studies to quantify uncertainties on simulated brightness temperatures (T b ) related to uncertainties on sea surface and scattering modeling. Using a two-scale sea surface emissivity model to simulate T b at L band (1.4 GHz), we explore the influence on estimated SSS of the parameterization of the seawater permittivity, of the sea wave spectrum, of the choice of the two-scale cutoff wavelength, and of adding swell to the wind sea. Differences between T b estimated with various existing permittivity models are up to 1.5 K. Therefore a better knowledge of the seawater permittivity at L band is required. The influence of wind speed on T b simulated with various parameterizations of the sea wave spectrum differs by up to a factor of two; for a wind speed of 7 m s À1 the differences on estimated SSS is several psu depending on the sea wave spectral model taken, so that sea spectrum is a major source of uncertainty in models. We find no noticeable effect on simulated T b when changing the two-scale cutoff wavelength and when adding swell to the wind sea for low to moderate incidence angles. The dependence of the wind-induced T b on SST and SSS being weak, we assess the error in SSS estimated assuming that the wind speed influence is independent of SST and SSS. We find errors on estimated SSS up to 0.5 psu for 20°C variation in SST. Therefore this assumption would induce regional biases when applied to global measurements.INDEX TERMS: 4275 Oceanography: General: Remote sensing and electromagnetic processes (0689); 4271 Oceanography: General: Physical and chemical properties of seawater; 0659 Electromagnetics: Random media and rough surfaces; KEYWORDS: microwave, radiometry, remote sensing, salinity, roughness Citation: Dinnat, E. P., J. Boutin, G. Caudal, and J. Etcheto, Issues concerning the sea emissivity modeling at L band for retrieving surface salinity,

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Section: Introductionsupporting

confidence: 88%

Issues concerning the sea emissivity modeling at L band for retrieving surface salinity

et al. 2003

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“…The L band antenna system was changed from a circular horn antenna to a 64-element phased array inside a thermally controlled radome enclosure. A theoretical calculation [Blume et al, 1977] of this new correction factor yielded a value of 0.17 K, which compares closely with the 0.14 K factor for the original antenna.…”

Section: ' Theory and Data Reductionsupporting

confidence: 65%

“…The corrections to the measured brightness temperature of the ocean surface can still be of the order of a few kelvins and, therefore, must be taken into account. The apparent temperature Te (which may also be called the equivalent radiometric temperature of the complete set of received radiations) is calculated from the equation of radiative transfer by making use of the Rayleigh-Jeans approximation to the Planck law [Blume et al, 1977].…”

Section: ' Theory and Data Reductionmentioning

confidence: 99%

Microwave radiometer measurement of tidally induced salinity changes off the Georgia coast

Kendall¹,

Blanton²

1981

J. Geophys. Res.

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A quasi‐synoptic survey of tidally induced salinity changes off the Georgia coast was performed by using a L band microwave radiometer onboard a NASA aircraft. Salinity maps were obtained for ebb and flood conditions in order to define the salinity distributions near rivers and sounds and major changes that occur from ebb flow to flood flow. The Savannah River plume dominated the salinity regime and extended out from the Savannah River mouth about 12 km during ebb tidal conditions. The plume merged into a band of low salinity water extending along the Georgia‐South Carolina coast which was produced by the many river sources of freshwater entering the coastal waters. The changes in salinity observed offshore of the river plume area were consistent with estimates of the changes that would occur over a typical tidal excursion perpendicular to the observed gradient.

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“…where p is the emissivity at polarization p ϭ h or v; p,0 is the emissivity at polarization p of an ideal, flat ocean surface using Stogryn (1997) for ocean dielectric constant; u is the neutral stability near-surface wind speed; and inc is the incidence angle in units of degrees. This model for wind-induced excess emissivity follows from Blume et al (1977) for nadir sensitivity, together with an estimated extrapolation to off-nadir incidence using a two-scale surface emission model (F. J. Wentz 2001, personal communication).…”

Section: Forward Model For Brightness Temperaturementioning

confidence: 99%

Vicarious Calibration of an Ocean Salinity Radiometer from Low Earth Orbit

Ruf

2003

J. Atmos. Oceanic Technol.

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Statistical properties of the brightness temperature (T B) measured by a low-earth-orbiting radiometer operating at 1.4 GHz are considered as a means of calibrating and validating the sensor. Mapping of ocean salinity by such an instrument requires that its calibration be extremely stable over time. Whether certain statistical properties of the measurements are stationary (time invariant) enough to be of value as benchmarks to which the calibration can be referenced is considered. The global minimum, maximum, and average T B are considered, together with a vicarious cold T B statistic that makes use of a sharp lower bound on naturally occurring values for T B. Examination of simulated global distributions of the T B measurements suggests several things about the stationarity (or lack thereof) of the statistics in question. Global minima can vary widely due to instrument noise and are not a reliable calibration reference. Global maxima are strongly influenced by a number of environmental factors as well as by instrument noise and are even less stationary than the minima. Global averages are largely insensitive to instrument noise and, in most cases, to environmental conditions as well. The global average T B varies at only the 0.1-K rms level except in cases of anomalously high winds, when it can increase considerably more. The vicarious cold T B is similarly insensitive to instrument effects and most environmental factors. It is not significantly affected by high wind conditions. The stability of the vicarious cold T B is, however, found to be sensitive at the several tenths of a kelvin level to variations in the background cold space brightness. The global average is much less sensitive to this parameter, so using the two approaches together should be mutually beneficial.

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

Cited by 24 publications

References 15 publications

Issues concerning the sea emissivity modeling at L band for retrieving surface salinity

Issues concerning the sea emissivity modeling at L band for retrieving surface salinity

Microwave radiometer measurement of tidally induced salinity changes off the Georgia coast

Vicarious Calibration of an Ocean Salinity Radiometer from Low Earth Orbit

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