[1] This article presents first results of deriving relative surface soil moisture from the METOP-A Advanced Scatterometer. Retrieval is based on a change detection approach which has originally been developed for the Active Microwave Instrument flown onboard the European satellites ERS-1 and ERS-2. Using model parameters derived from eight years of ERS scatterometer data, first global soil moisture maps have been produced from ASCAT data. The ASCAT data were distributed by EUMETSAT for validation purposes during the ASCAT product commissioning activities. Several recent cases of drought and excessive rainfall are clearly visible in the soil moisture data. The results confirm that seamless soil moisture time series can be expected from the series of two ERS and three METOP scatterometers, providing global coverage on decadal time scales (from 1991 to about 2021). Thereby, operational, nearreal-time ASCAT soil moisture products will become available for weather prediction and hydrometeorological applications.
The first operational European polar meteorological satellite system provides greatly enhanced capabilities, in particular for hyperspectral infrared atmospheric sounding and atmospheric trace gas monitoring.
International audienceThe Ocean Surface Topography Mission/Jason-2 (OSTM/Jason-2) satellite altimetry mission was successfully launched on June 20, 2008, as a cooperative mission between CNES, EUMETSAT, NASA, and NOAA. OSTM/Jason-2 will continue to precisely measure the surface topography of the oceans and continental surface waters, following on the same orbit as its predecessors, TOPEX/Poseidon and Jason-1. To maintain the high-accuracy measurements, the mission carries a dual-frequency altimeter, a three-frequency microwave radiometer, and three precise positioning systems. The objectives of the mission are both operational and scientific. The mission will provide near-real time high-precision altimetric measurements for integration into ocean forecasting models and other products. The mission will also extend the precise surface topography time series started by TOPEX/Poseidon in 1992 over two decades in order to study long-term ocean variations such as mean sea level variations and interannual and decadal oscillations. The measurement system has been adapted to provide quality data nearer to the coasts, and over lakes and rivers. This paper provides an overview of the OSTM/Jason-2 mission in terms of the system design and a brief introduction to the science objectives
The paper gives an overview of the development of satellite oceanography over the past five years focusing on the most relevant issues for operational oceanography. Satellites provide key essential variables to constrain ocean models and/or serve downstream applications. New and improved satellite data sets have been developed and have directly improved the quality of operational products. The status of the satellite constellation for the last five years was, however, not optimal. Review of future missions shows clear progress and new research and development missions with a potentially large impact for operational oceanography should be demonstrated. Improvement of data assimilation techniques and developing synergetic use of high resolution satellite observations are important future priorities.
The Advanced Scatterometer (ASCAT) onboard the Metop-A satellite became operational shortly after launch in 2006, and an absolute calibration using three transponders was achieved in November 2008. In this paper, we describe how the CMOD5.n ocean backscatter geophysical model function (GMF), which was derived using data from previous scatterometers onboard the European Remote Sensing 1 and 2 satellites (ERS-1 and ERS-2), was used to derive backscatter bias correction factors. The purpose is to remove the bias between ASCAT backscatter data and the CMOD5.n GMF output which allows these data to be used in place of ERS data in existing wind processing algorithms. The ASCAT Wind Data Processor, developed at the Royal Netherlands Meteorological Institute (KNMI), applies the bias correction factors to ASCAT data and uses CMOD5.n to retrieve wind vectors in order to produce an operational wind product. This resulted in a stable and high-quality ASCAT wind product since February 2007. We validate this product by comparing it to the European Centre for Medium-range Weather Forecasts (ECMWF) winds and buoy measurements. The bias correction factors indicate that ASCAT data and the GMF differ by roughly 0.3 dB below 55 • and up to 0.8 dB above 55 •. A possible explanation lies in CMOD5.n which has been poorly validated in this incidence angle regime. Validation of ASCAT data using the ocean calibration method confirms this result and also indicates that bias-corrected data are everywhere within 0.3 dB of CMOD5.n. The wind product validation shows an rms error of 1.3 m • s −1 in wind speed and 16 • in wind direction when compared to ECMWF winds. This is better than the results achieved using ERS scatterometer data. Against buoy winds, we find an rms error wind component error of approximately 1.8 m • s −1. These results show that the ASCAT wind product is of high quality and satisfies its wind component accuracy requirement of 2 m • s −1 .
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