Hans Bonekamp

Initial soil moisture retrievals from the METOP‐A Advanced Scatterometer (ASCAT)

[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 MicrowaveInstrument flownonboardtheEuropeansatellites 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. Citation: Bartalis, Z., W. Wagner, V. Naeimi, S. Hasenauer, K. Scipal, H. Bonekamp, J. Figa, and C. Anderson (2007), Initial soil moisture retrievals from the METOP-A Advanced Scatterometer (ASCAT), Geophys. Res. Lett., 34, L20401, doi:10.1029/2007GL031088.

An Introduction to the EUMETSAT Polar system

Abstract The European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Polar System is the European contribution to the European–U.S. operational polar meteorological satellite system (Initial Joint Polar System). It serves the midmorning (3.3.) orbit 0930 Local Solar Time (LST) descending node. The EUMETSAT satellites of this new polar system are the Meteorological Operational Satellite (Metop) satellites, jointly developed with ESA. Three Metop satellites are foreseen for at least 14 years of operation from 2006 onward and will support operational meteorology and climate monitoring. The Metop Programme includes the development of some instruments, such as the Global Ozone Monitoring Experiment, Advanced Scatterometer, and the Global Navigation Satellite System (GNSS) Receiver for Atmospheric Sounding, which are advanced instruments of recent successful research missions. Core components of the Metop payload, common with the payload on the U.S. satellites, are the Advanced Very H...

Validation and Calibration of ASCAT Using CMOD5.n

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.

The OSTM/Jason-2 Mission

The 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.

Radiometric Calibration of the Advanced Wind Scatterometer Radar ASCAT Carried Onboard the METOP-A Satellite

The Advanced Wind Scatterometer (ASCAT) is a six-beam spaceborne radar instrument designed to measure wind fields over the oceans. An ASCAT instrument is carried by each of the three METOP satellites. The ASCAT calibration strategy is described and detailed results are presented concerning the radiometric calibration achieved.

Validation of Backscatter Measurements from the Advanced Scatterometer on MetOp-A

The Advanced Scatterometer (ASCAT) on the Meteorological Operational (MetOp) series of satellites is designed to provide data for the retrieval of ocean wind fields. Three transponders were used to give an absolute calibration and the worst-case calibration error is estimated to be 0.15‐0.25 dB. In this paper the calibrated data are validated by comparing the backscatter from a range of naturally distributed targets against models developed from European Remote Sensing Satellite (ERS) scatterometer data. For the Amazon rainforest it is found that the isotropic backscatter decreases from 26.2 to 26.8 dB over the incidence angle range. The ERS value is around 26.5 dB. All ASCAT beams are within 0.1 dB of each other. Rainforest backscatter over a3-yr period is found tobeverystablewithannualchangesof approximately0.02 dB. ASCAT ocean backscatter is compared against values from the C-band geophysical model function (CMOD-5) using ECMWF wind fields. A difference of approximately 0.2 dB below 558 incidence is found. Differences of over 1 dB above 558 are likely due to inaccuracies in CMOD-5, which has not been fully validated at large incidence angles. All beams are within 0.1 dB of each other. Backscatter from regions of stable Antarctic sea ice is found to be consistent with model backscatter except at large incidence angles where the model has not been validated. The noise in the ice backscatter indicates that the normalized standard deviation of the backscatter values Kp is around 4.5%, which is consistent with the expected value. These results agree well with the expected calibration accuracy and give confidence that the calibration has been successful and that ASCAT products are of high quality.

Status of the Metop ASCAT soil moisture product

Since December 2008 the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) has been disseminating global 25 km ASCAT surface soil moisture data in near real-time (within 135 minutes after sensing) over its broadcast system EUMETCast. The ASCAT surface soil moisture product is thus the first truly operational satellite soil moisture product that may be used for Numerical Weather Prediction (NWP), flood forecasting and other time-critical applications. In this paper we provide information about the status of the ASCAT Level 2 soil moisture processor, review first published validation and application studies and discuss plans for further improvements.

Analysis of ASCAT Ocean Backscatter Measurement Noise

The Advanced Scatterometer (ASCAT) level 1b products provide spatially averaged calibrated backscatter measurements along with their Kp values which are estimates of the normalized standard deviation of the backscatter values. The Kp values can be regarded as a measure of the error in the mean backscatter caused by speckle noise, instrument characteristics, data processing, and spatial inhomogeneities of the target. This information assists in the retrieval of wind vectors and allows their error characteristics to be determined. This paper describes the algorithm used to calculate Kp. The algorithm considers both the correlations that occur in ASCAT data due to onboard processing and the Hamming weights used in the spatial averaging in the ground processing. ASCAT Kp values over the open ocean are investigated, and we demonstrate that their behavior is as expected and meets requirements. This indicates that the ASCAT instrument is operating as intended and is providing good quality ocean backscatter data. The behavior of Kp over Arctic sea ice is also examined, and we show that it contains geophysical information that may be useful for various applications such as ice-type classification or sea ice tracking.

OSTM/Jason-2: Assessment of the System Performances (Ocean Surface Topography Mission: OSTM)

On June 20, 2008, Jason-2 was successfully launched by a Boeing Delta II rocket from the Vandenberg site, California. The OSTM/Jason-2 project is a cooperation among NASA, NOAA, EUMETSAT, and CNES. The first two months of the OSTM/Jason-2 mission have been dedicated to the assessment of the overall system. The goal of this assessment phase was: i. to assess the behavior of the spacecraft, at the platform and payload levels; ii. to verify that platform performance requirements are met with respect to Jason-2 requirements; iii. to verify that payload instruments performance requirements evaluated at instrument level are met; and iv. to assess the performance of the Jason-2 Ground System. The paper will display the main outputs of the assessment of the system. It will demonstrate that all the elements of the onboard and ground systems are within the specifications.

Validation of Coarse Resolution Microwave Soil Moisture Products

The strong relationship between soil moisture content and the soil dielectric constant offers a direct way of measuring soil moisture with microwave sensors. Global coarse-resolution soil moisture datasets are currently retrieved from active microwave spaceborne instruments (AMI onboard ERS and ASCAT on Metop-A) and in the near future from dedicated passive microwave satellite sensors (SMOS). This article summarizes recent soil moisture research activities and briefly discusses the strategies for validation and cross-comparison of remotely sensed soil moisture datasets. Special attention is given to the first validation of the soil moisture data from the ASCAT instrument on Metop-A in relation to the absolute and relative calibrations of the instrument. A first assessment of the quality of the ASCAT surface soil moisture is given by studies of stable targets and the spatial and temporal extent of recent extreme drought and rainfall events.