Abstract
Abstract. The microwave radiometers (MWRs) on board the European Remote Sensing Satellites 1 and 2 (ERS-1 and ERS-2) and Envisat provide a continuous time series of brightness temperature observations between 1991 and 2012. Here we report on a new total column water vapour (TCWV) and wet tropospheric correction (WTC) dataset that builds on this time series. We use a one-dimensional variational approach to derive TCWV from MWR observations and ERA-Interim background information. A particular focus of this study lies on the intercalibration of the three different instruments, which is performed using constraints on liquid water path (LWP) and TCWV. Comparing our MWR-derived time series of TCWV against TCWV derived from Global Navigation Satellite System (GNSS) we find that the MWR-derived TCWV time series is stable over time. However, observations potentially affected by precipitation show a degraded performance compared to precipitation-free observations in terms of the accuracy of retrieved TCWV. An analysis of WTC shows further that the retrieved WTC is superior to purely ERA-Interim-derived WTC for all satellites and for the entire time series. Even compared to the European Space Agency's (ESA) operational WTC retrievals, which incorporate in addition to MWR additional observational data, the here-described dataset shows improvements in particular for the mid-latitudes and for the two earlier satellites, ERS-1 and ERS-2. The dataset is publicly available under doi:10.5676/DWD_EMIR/V001 (Bennartz et al., 2016).
Highlights
ESA’s altimetry missions are at the heart of significant progress on oceanography
This publication is organized as follows: in Sect. 2 we describe the microwave radiometers (MWRs) brightness temperature time series as well as the methods used for retrieving total column water vapour (TCWV) and wet tropospheric correction (WTC)
The Envisat MWR brightness temperatures underlying the have been generated by Collecte Localisation Satellite (CLS) in 2014 in the framework of the Envisat MWR L1B Expert Support Laboratory (ESL) activities funded by ESA
Summary
ESA’s altimetry missions are at the heart of significant progress on oceanography. The combined coverage of highquality observations by the European Remote Sensing Satellites 1 and 2 (ERS-1 and ERS-2) and Envisat spans over more than 20 years from 1991 to 2012. To provide the observations required for the WTC is the primary role of the nadirlooking microwave radiometer (MWR) embedded into the altimetry missions on board ERS-1, ERS-2, and Envisat. In this context, requirements on accuracy, sensitivity, and longterm stability of the atmospheric water vapour observations are strong since altimetry missions require a precision better than 1 cm in WTC (Eymard et al, 2005) and a temporal stability better than 1 mm yr−1 (Ablain et al, 2009). The sensitivity of the retrieval with respect to the background (a priori) temperature and water vapour profiles is discussed in the Appendix
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