Abstract
Abstract The wet tropospheric path delay is presently the main source of error in the estimation of the mean sea level by satellite altimetry. This correction on altimetric measurements, provided by a dedicated radiometer aboard the satellite, directly depends on the atmospheric water vapor content. Nowadays, water vapor products from microwave radiometers are rather consistent but important discrepancies remain. Understanding these differences can help improve the retrieval of water vapor and reduce at the same time the error on the mean sea level. Three radiometers are compared: the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E), Jason-1 microwave radiometer (JMR), and Envisat microwave radiometer (MWR). Water vapor products are analyzed both in terms of spatial and temporal distribution over the period 2004–10, using AMSR-E as a reference. The Interim ECMWF Re-Analysis (ERA-Interim) data are also included in the study as an additional point of comparison. Overall, the study confirms the general good agreement between the radiometers: similar patterns are observed for the spatial distribution of water vapor and the correlation of the times series is better than 0.90. However, regional discrepancies are observed and a quantitative agreement on the trend is not obtained. Regional discrepancies are driven by the annual cycle. The JMR product shows discrepancies are highly dependent on water vapor, which might be related to calibration issues. Furthermore, triple collocation analysis suggests a possible drift of JMR. MWR discrepancies are located in coastal regions and follow a seasonal dynamic with stronger differences in summer. It may result from processing of the brightness temperatures.
Highlights
IntroductionThe mean sea level evolution is monitored and studied using tide gauge records, satellite altimetry measurements, and numerical models
The ocean mean sea level (MSL) is a key indicator of the global warming
This paper presents the comparison of independent water vapor products from three radiometers: AMSR-E on Aqua, Jason-1 microwave radiometer (JMR) on Jason-1, and RA2-microwave radiometer (MWR) on Envisat, for the period 2004–10
Summary
The mean sea level evolution is monitored and studied using tide gauge records, satellite altimetry measurements, and numerical models. Models are often combined with observations through assimilation techniques to Exploitation of altimetry measurements over ocean depends on the feasibility of correcting the altimeter range for different perturbations. The wet tropospheric correction, is nearly proportional to the integrated water vapor and is provided by a dedicated instrument, a microwave radiometer, operating around the water vapor absorption line (22 GHz). The uncertainty in this correction is today a major part of the global mean sea level trend error budget. Any error in the wet path delay impacts directly the estimation of the sea level. Ablain et al (2009) have estimated
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