Remote sensing of Antarctic sea ice is required to characterize properties of the vast sea ice cover to understand its long-term increase in contrast to the decrease of Arctic sea ice. For this objective, the OIB/TanDEM-X Coordinated Science Campaign (OTASC) was successfully conducted in 2017 to obtain contemporaneous and collocated remote sensing data from NASA's Operation IceBridge (OIB) and the German Aerospace Center (DLR) TanDEM-X Synthetic Aperture Radar (SAR) system at X band together with Sentinel-1 and RADARSAT-2 SARs at C band in conjunction with WorldView satellite spectral sensors, surface measurements, and field observations. The Weddell Sea and the Ross Sea were two primary regions while SAR data were also collected over six other regions in the Southern Ocean. Satellite SAR data included both polarimetric and interferometric capabilities to infer snow and sea ice information in three dimensions (3D), while OIB/P-3 aircraft data include snow radar together with altimeter data for snow and sea ice observations in 3D over the Weddell Sea. Across the Ross Sea, IcePOD and AntNZ/York-University flights were carried out together with satellite SAR data acquisitions.

The L-band passive and active microwave geophysical model functions (GMFs) of ocean surface winds from the Aquarius data are derived. The matchups of Aquarius data with the Special Sensor Microwave Imager (SSM/I) and National Centers for Environmental Prediction (NCEP) winds were performed and were binned as a function of wind speed and direction. The radar HH GMF is in good agreement with the PALSAR GMF. For wind speeds above 10 m·s-1, the L-band ocean backscatter shows positive upwind-crosswind (UC) asymmetry; however, the UC asymmetry becomes negative between about 3 and 8 m·s-1. The negative UC (NUC) asymmetry has not been observed in higher frequency (above C-band) GMFs for ASCAT or QuikSCAT. Unexpectedly, the NUC symmetry also appears in the L-band radiometer data. We find direction dependence in the Aquarius TBV, TBH, and third Stokes data with peak-to-peak modulations increasing from about a few tenths to 2 K in the range of 10-25- m·s-1wind speed. The validity of the GMFs is tested through application to wind and salinity retrieval from Aquarius data using the combined active-passive algorithm. Error assessment using the triple collocation analyses of SSM/I, NCEP, and Aquarius winds indicates that the retrieved Aquarius wind speed accuracy is excellent, with a random error of about 0.75 m·s-1. The wind direction retrievals also appear reasonable and accurate above 10 m·s-1. The results of the error analysis indicate that the uncertainty of the GMFs for the wind speed correction of vertically polarized brightness temperatures is about 0.14 K for wind speed up to 10 m·s-1.

An elongated sea ice feature called the Svalbard sea ice barrier rapidly formed over an area in the Barents Sea to the east of Svalbard posing a significant navigational hazard. The secret of this sea ice formation lies in the bottom bathymetry, which governs the distribution of cold Arctic waters masses and sea ice growth

The Jet Propulsion Laboratory NUSCAT K/sub u/-band scatterometer successfully acquired ocean backscatter data over a wide variety of oceanic and atmospheric conditions during the Surface Wave Dynamics Experiment (SWADE). Ten flights resulted in 30 h of data collection were conducted on the NASA Ames C130 aircraft. The SWADE experimental area was deployed with several buoys providing appropriate in situ measurements to correlate with the radar backscatter for incidence angles from 10 to 60/spl deg/ at both horizontal and vertical polarizations. The NUSCAT-SWADE backscatter data base was utilized in conjunction with buoy measurements to investigate ocean backscatter signatures over the range of conditions encountered during SWADE. To account for modulations and fluctuations in incidence angles, a backscatter analysis independent of a priori geophysical model functions was developed, tested, and implemented. Results for backscatter azimuth modulations in terms of upwind, downwind, and crosswind radar returns are compared to airborne RADSCAT results and to SASS-I and II geophysical model functions versus neutral wind speed (U/sub N/). NUSCAT-SWADE results are closest overall to SASS-II values, fit best with SASS-I at 10/spl deg/ incidence angle, and are significantly higher than RADSCAT. Effects of friction velocity (u*), wave age (c/sub o//u*), and significant wave height (H/sub 1/3/) on ocean backscatter are studied. The backscatter shows a good positive sensitivity to u*, an inverse dependence on c/sub o//u*, and no systematic trend with H/sub 1/3/ excluding cases of large swells. Coefficients of empirical relations between backscatter and neutral wind speed, friction velocity, and wave age are derived for 10-40/spl deg/ incidence angles at both horizontal and vertical polarizations. Covariance studies of backscatter with the derived relations to winds show an overall deviation factor in the order of 1 dB for ocean signatures including uncertainties in surface conditions.

Ocean radar backscatter in the presence of large waves is investigated using data acquired with the Jet Propulsion Laboratory NUSCAT radar at Ku band for horizontal and vertical polarizations and the University of Massachusetts C-SCAT radar at C band for vertical polarization during the Surface Wave Dynamics Experiment. Off-nadir backscatter data of ocean surfaces were obtained in the presence of large waves with significant wave height up to 5.6 m. In moderate-wind cases, effects of large waves are not detectable within the measurement uncertainty and no noticeable correlation between backscatter coefficients and wave height is found. Under high-wave light-wind conditions, backscatter is enhanced significantly at large incidence angles,with a weaker effect at small incidence angles. Backscatter coefficients in the wind speed range under consideration are compared with SASS-II (Ku band), CMOD3-H1 (C band), and Plant's model results which confirm the experimental observations. Variations of the friction velocity, which can give rise to the observed backscatter behaviors in the presence of large waves, are presented.>

Attempting to understand and predict weather on a local and global basis has challenged both the scientific and engineering communities. One key parameter in understanding the weather is the ocean surface wind vector because of its role in the energy exchange at the air-sea surface. scatterometers, radars that measure the reflectivity of a target offer a tool with which to remotely monitor these winds from tower-, aircraft-, and satellite-based platforms. This paper introduces three current airborne scatterometer systems, and presents data collected by these instruments under low-, moderate-, and high-wind conditions. The paper focuses on airborne scatterometers because of their ability to resolve submesoscale variations in wind fields. Discrepancies between existing theory and the observations are noted and the concerns in measuring low-wind speeds discussed. Finally, the application of using this technology for estimating the surface-wind vector during a hurricane is demonstrated.>