HelioFTH: combining cloud index principles and aggregated rating for cloud masking using infrared observations from geostationary satellites

B Dürr,R Posselt,M Schröder,R Stöckli

doi:10.5194/amt-6-1883-2013

Abstract

Abstract. In this paper a cloud mask and cloud fractional coverage (CFC) retrieval scheme called HelioFTH is presented. The algorithm is self-calibrating and relies on infrared (IR) window-channel observations only. It needs no input from numerical weather prediction (NWP) or radiative transfer models, nor from other satellite platforms. The scheme is applicable to the full temporal and spatial resolution of the Meteosat Visible and InfraRed Imager (MVIRI) and the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) sensors. The main focus is laid on the separation of middle- and high-level cloud coverage (HCC) from low-level clouds based on an internal cloud-top pressure (CTP) product. CFC retrieval employs a IR-only cloud mask based on an aggregated rating scheme. CTP retrieval is based on a Heliosat-like cloud index for the MVIRI IR channel. CFC from HelioFTH, the International Satellite Cloud Climatology Project (ISCCP) DX and the Satellite Application Facility on Climate Monitoring (CM SAF) were validated with CFC from the Baseline Surface Radiation Network (BSRN) and the Alpine Surface Radiation Budget (ASRB) network. HelioFTH CFC differs by not more than 5–10% from CM SAF CFC but it is higher than ISCCP-DX CFC. In particular the conditional probability to detect cloud-free pixels with HelioFTH is raised by about 35% compared to ISCCP-DX. The HelioFTH CFC is able to reproduce the day-to-day variability observed at the surface. Also, the HelioFTH HCC was inter-compared to CM SAF and ISCCP-DX over different regions and stations. The probability of false detection of cloud-free HCC pixels is in the same order as ISCCP-DX compared to the CM SAF HCC product over the full-disk area. HelioFTH could be used for generating an independent climate data record of cloud physical properties once its consistency and homogeneity is validated for the full Meteosat time series.

Highlights

Hydrology and Earth System level clouds based on an internal cloud-top pressure (CTP) Clouds play an essential role in Sdecteiremnincineg sthe earth’s radiproduct.ation balance
HelioFTH CTP, Cloud Fractional Cover (CFC) and high-level cloud coverage (HCC) is intercompared to the corresponding ISCCP-DX and CM SAF products
We used the definition of statistical quantities as defined in Appendix A suggested by Reuter et al (2009, see Sect. 5), who compared CM SAF CFC with synoptic reports (SYN) for the year 2006

Summary

Introduction

Hydrology and Earth System level clouds based on an internal cloud-top pressure (CTP) Clouds play an essential role in Sdecteiremnincineg sthe earth’s radiproduct. They are essential factors regulating the global. CFC retrieval employs a IR-only cloud mask based on water cycle. CTP retrieval is based on a tainty of modeled climate predictions is related to the feed-. Heliosat-like cloud index for the MVIRI IR channel. CFC from HelioFTH, the International Satellite Cloud Climatol-. FTchloeudausttoomgarteeedOnhidoceuensteaifigncaastSicohcnaineogfnesccl(oeTurdesnbienrtshateetllailt.e, ogy Project (ISCCP) DX and the Satellite Application Fa- measurements is a challenging task and a basic requirement cility on Climate Monitoring (CM SAF) were validated with for processing of cloudy and clear sky products.

Methods

Results

Conclusion