Abstract
Abstract. The second generation of the EUMETSAT Polar System (EPS-SG) will include the Ice Cloud Imager (ICI), the first operational sensor covering sub-millimetre wavelengths. Three copies of ICI will be launched that together will give a measurement time series exceeding 20 years. Due to the novelty of ICI, preparing the data processing is especially important and challenging. This paper focuses on activities related to the operational product planned, but also presents basic technical characteristics of the instrument. A retrieval algorithm based on Bayesian Monte Carlo integration has been developed. The main retrieval quantities are ice water path (IWP), mean mass height (Zm) and mean mass diameter (Dm). A novel part of the algorithm is that it fully presents the inversion as a description of the posterior probability distribution. This is preferred for ICI as its retrieval errors do not always follow Gaussian statistics. A state-of-the-art retrieval database is used to test the algorithm and to give an updated estimate of the retrieval performance. The degrees of freedom in measured radiances, and consequently the retrieval precision, vary with cloud situation. According to present simulations, IWP, Zm and Dm can be determined with 90 % confidence at best inside 50 %, 700 m and 50 µm, respectively. The retrieval requires that the data from the 13 channels of ICI are remapped to a common footprint. First estimates of the errors introduced by this remapping are also presented.
Highlights
Satellite data are today an indispensable part of numerical weather prediction (NWP); see for example Bauer et al (2015)
The planned output of the EUMETSAT Polar System – Second Generation (EPS-SG) Overall Ground Segment at EUMETSAT Headquarters includes the MWI-ICIL2 product, which will contain retrievals based on MWI and Ice Cloud Imager (ICI) and be delivered in near real time
Additional products from ICI will be generated directly by the Satellite Application Facilities (SAFs) located at weather services in EUMETSAT member and co-operating states
Summary
Satellite data are today an indispensable part of numerical weather prediction (NWP); see for example Bauer et al (2015). P. Eriksson et al.: Towards an operational ICI retrieval product (Special Sensor Microwave – Imager), introduced in 1987, had humidity, cloud liquid water and precipitation as the main atmospheric targets, with channels at 19.4, 22.2, 37.0 and 85.5 GHz (see for example Schluessel and Emery, 1990), and extended the coverage of the microwave region to higher frequencies. CIWSIR was not selected, but ESA funded preparatory studies that lead to a consolidated mission proposal called CloudIce for Earth Explorer 8 in 2010 (Buehler et al, 2012) It featured channels near 183.31, 243.20, 325.15, 448.00 and 664.00 GHz. Shortly thereafter, a similar sensor was proposed for the international space station (ISS-ICE), with a reduced set of channels.
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