Vladimir G. Irisov

The analysis of wind exponents retrieved from microwave radar and radiometric measurements

The analysis of the dependence of gravity-capillary spectral density on wind speed is based on near-nadir microwave radiometric measurements and VV scatterometric measurements at view angles 30/spl deg/-60/spl deg/ from nadir obtained by different investigators in field experiments during the last 25 years. Wind exponents estimated by a symmetric-regression technique for moderate wind speed are consistent both for radiometric and scatterometric measurements. Using Donelan and Piersons approach, a parameterization of the exponent in the nonlinear dissipation term is derived. The results obtained can be used in model development for the purposes of microwave remote sensing of the ocean.

Passive acoustic measurements of wind velocity and sound speed in air

Random acoustic fields generated by uncorrelated sources in moving media contain information about the propagation environment, including sound speed and flow velocity. This information can be recovered by noise interferometry. Here interferometric techniques are applied to road traffic noise. Acoustic travel times and their nonreciprocity are retrieved from two-point cross-correlation functions of noise. The feasibility of passive acoustic measurements of wind velocity using diffuse noise is experimentally demonstrated for the first time. The accuracy of the interferometric measurements of sound speed and wind velocity is confirmed by comparison with in situ measurements of wind, air temperature, and humidity.

Microwave polarimetric measurements of the sea surface brightness temperature from a blimp during the Coastal Ocean Probing Experiment (COPE)

Experimental data obtained with a microwave dual-frequency radiometer at 23.87 and 31.65 GHz and a polarimeter at 37.0 GHz installed on a blimp during the Coastal Ocean Probing Experiment in 1995 are analyzed. Observations of the downwelling atmospheric radiation as a function of angle were used to achieve a highly accurate absolute calibration. The dependence of the sea surface brightness temperature on nadir and azimuthal angles is considered. The experimental data are compared with theoretical calculations based on several models of sea wave spectra. Models proposed by Romeiser et al. [1997] and Elfouhaily et al. [1997] fit well to the COPE azimuthal measurements and data averaged over azimuthal angle are in between of values predicted by spectrum models by Apel [1994] and Elfouhaily et al. [1997]. The conclusion is made about high sensitivity of the polarized radiometric measurements to parameters of gravity-capillary spectrum.

Sea‐air and boundary layer temperatures measured by a scanning 5‐mm‐wavelength radiometer: Recent results

A scanning 5-mm-wavelength (60 GHz) radiometer was deployed during two recent experiments. The first was in September–October in 1995 when the Environmental Technology Laboratory conducted the Coastal Ocean Probing Experiment off the Oregon coast. During this experiment the scanning radiometer was deployed on the Floating Instrument Platform, a research vessel operated by the Scripps Institution of Oceanography. Ground truth for the radiometer was provided by two independent in situ and infrared measurements of the ocean surface temperature; ground truth for air temperature was also provided by two in situ measurements at 0.5 and 12 m above the ocean surface. The second experiment was during September 10–30, 1996, at the Department of Energys Atmospheric Radiation Measurement Programs Cloud and Radiation Testbed site near Lamont, Oklahoma. Here ground truth for derived quantities consisted of 3-hourly radiosonde releases and measurements at 25 and 60 m from a meteorological tower. The results of the experiments indicate that the scanning radiometer yields accuracies of the order of 0.4°C rms for sea-air temperature difference and accuracies in temperature of better than 0.7°C rms at altitudes below 60 m.

Remote sensing of boundary-layer temperature profiles by a scanning 5-mm microwave radiometer and RASS: a comparison experiment

Two techniques for deriving low-altitude temperature profiles were evaluated at an experiment conducted from November 1996 to January 1997 at the Boulder Atmospheric Observatory (BAO). The first used a scanning single wavelength 5-mm (60 GHz) microwave radiometer to measure vertical temperature profiles. The second was a Radio Acoustic Sounding System (RASS) that operated at 915 MHz. Typically, radiometric profiles were produced every 15 min; those from RASS were hourly. The BAO has an instrumented 300-m tower with 5-min measurements of temperature and relative humidity available at the surface and at altitudes of 10, 50, 100, 200, and 300 m. The tower measurements were occasionally supplemented with radiosonde releases and with hand-held meteorological measurements taken on the tower elevator. Data from this experiment are presented and plans for future deployments of these instruments are discussed. In addition, a new quality control algorithm for the RASS system is presented and evaluated.

Comparison of scatterometer and radiometer wind vector measurements

Abstract Coincident measurements with a 37-GHz polarimetric radiometer and a 10-GHz scatterometer during the Coastal Ocean Probing Experiment (COPE) in September and October of 1995 offered a unique opportunity to compare their relative sensitivity and performance in observing sea surface winds. The scatterometer cross section σo and the radiometers second and third Stokes parameters, Q and U, were measured. The dependence of the angular signature of the radiometer on friction velocity was investigated by combining the COPE data with data collected in the Labrador Sea in February and March of 1997 at higher wind speeds than were encountered during COPE. The results of these experiments showed that the first harmonics of the radiometer azimuthal response were relatively insensitive to the friction velocity but that their second harmonics increased rapidly in amplitude with increasing friction velocity, with approximately the same sensitivity as a scatterometer cross section. The sensitivity of the radar a...

Wind dependences of brightness temperature measured by airborne Ka-band polarimeter during the Shoaling Waves Experiment

Airborne Ka-band radiometric observations of the ocean were used to derive wind dependences of brightness temperature at various viewing angles. Brightness temperature contrast appeared to be significantly higher than predicted by Elfouhailys spectrum and small slope approximation.

Electromagnetic Model for Rough Sea Surface Microwave Emission and Reconstruction of Ripple Spectrum Parameters

ABaRACT The two scale model of sea surface brightness temperature is considered. The microwave emission of gravitational-capillary part of sea wave spectrum is calculated by using perturbation technique and large scale waves are taken into account by averaging the emission from locally flat sloped squares. The resonant effects in thermal radiation formed by individual harmonics of ripple spectrum permits to recover from multichannel radiometric data parameters of spatial sea ripple spectrum. The reconstructed one in such way from large amount airborne measured radiometric data reveals good agreement with that obtained from radar data.

Radiometric Model of the Sea Surface in the Presence of Currents

A consistent radiometric model of the ocean is an important part of the interpretation of passive microwave radiometric data. Empirical relations between measured brightness temperature and environmental parameters such as wind, surface temperature, salinity, etc., are often used for processing satellite and airborne data. There are some difficulties when using these approaches when a nonstationary environment is being studied, such as wind and/or surface currents that vary in time and space. In this case, a consistent model based on physical parameters of the sea surface and atmosphere is needed. We consider a radiometric model of the ocean based on a wave-action balance equation. Following Kudryavtsev and Makin, we modified the source term to account for parasitic ripples. Along with surface roughness, the model provides wave-breaking statistics and foam coverage, which is especially important for the microwave radiometry due to high foam emissivity. Comparison between the model prediction and the experimental observations shows a good agreement.

An interference mitigation technique for passive remote sensing of soil moisture

Anthropgenic interference from terrestrial sources of microwave emission have been observed in passive Cband radiometric data using both the NOAA Environmental Technology Laboratory’s (ETL) PSR/CX airborne imaging instrument, and the JAXA AMSR-E instrument on the NASA EOS Aqua satellite. Simultaneous observations using multiple ~300 MHz subbands, incorporated into the PSR/CX instrument, have provided one means of interference mitigation that is useful under moderately contaminated conditions. ETL has developed a new C-band spectrometer that observes emissions within relatively narrower bandwidths and is tunable from 5.8 to 7.5 GHz. The spectrometer is able to reduce the effects of the interference at the expense of radiance sensitivity and observation time. Preliminary data analysis suggests the spectrometer to be an effective component for improving the accuracy of remotely sensed soil moisture measurements using C-band radiometry.