In this paper, we review the use of satellite-based remote sensing in combination with in situ data to inform Earth surface modelling. This involves verification and optimization methods that can handle both random and systematic errors and result in effective model improvement for both surface monitoring and prediction applications. The reasons for diverse remote sensing data and products include (i) their complementary areal and temporal coverage, (ii) their diverse and covariant information content, and (iii) their ability to complement in situ observations, which are often sparse and only locally representative. To improve our understanding of the complex behavior of the Earth system at the surface and sub-surface, we need large volumes of data from high-resolution modelling and remote sensing, since the Earth surface exhibits a high degree of heterogeneity and discontinuities in space and time. The spatial and temporal variability of the biosphere, hydrosphere, cryosphere and anthroposphere calls for an increased use of Earth observation (EO) data attaining volumes previously considered prohibitive. We review data availability and discuss recent examples where satellite remote sensing is used to infer observable surface quantities directly or indirectly, with particular emphasis on key parameters necessary for weather and climate prediction. Coordinated high-resolution remote-sensing and modelling/assimilation capabilities for the Earth surface are required to support an international application-focused effort.

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During the ERS-1 and ERS-2 missions, the application of synthetic aperture radar interferometry (InSAR) become known as a very important method for topographic mapping and high accuracy surface displacement measurements. Further investigations, however, showed that the expected accuracy could not be achieved in practice. It appeared that radiowave propagation heterogeneities through the atmosphere cause significant distortion to the observed signal and consequently to the derived topography and/or deformation signal. Inversely, it was shown that if topography is known and deformation is absent, the InSAR observations can be used to derive very accurate information on the state of atmosphere at the time of measurements. Due to the co-existence of MERIS (Medium Resolution Imaging Spectrometer) and ASAR (advanced synthetic aperture radar) on board of ENVISAT and the fact that their acquisitions can be collocated both in time and space, there are unique opportunities for complementary analysis. In this work we compare MERIS water vapor products and the integrated precipitable water vapor as observed with ASAR. Three complementary applications of the sensors are discussed. First, this is the correction of the atmospheric phase screen in InSAR products using the MERIS-derived water vapor signal. Second, we discuss the possibility for validating the MERIS water vapor product using InSAR data. Finally, we comment on the joint estimation of water vapor above and below the top of the cloud layers.@en