Introduction

Different algorithms for retrieving ice concentration from multichannel microwave radiometer measurements have evolved since the early eighties. These algorithms often differ in the channel selection and the way to handle geophysical influence, which represents effects like temperature, wind, water vapor etc.
Here, a total of 5 radiometer algorithms are compared on real microwave radiometer data. The algorithms cover the most widely used algorithms in literature, which includes AES [Swift et al., 1985], NORSEX [Svendsen et al., 1983], COMISO [Comiso, 1986] and NASA [Gloersen and Cavalieri, 1986]. They differ in the selection of channels, and the way they account for the atmosphere. The individual channels will be identified by the frequency in GHz and the polarization as V or H for vertical or horizontal, e.g., 37H identifies the channel with horizontal polarization and a frequency of 37GHz.
The COMISO algorithm is used with the 37V and 37H channels, in which case it is called the COMPOL algorithm, whereas it is called COMFREQ, when the channels are 37V and 19V. The data are recorded on the US-DMSP Special Sensor Microwave/Imager (SSM/I) program, processed into brightness temperature grids and delivered on CD-roms by [NSIDC]. The algorithms are tested for the total ice concentration (C) and the multi-year ice fraction given by

where is the multi-year ice fraction and is the amount of multi-year ice. Mean values and standard deviations of the ice concentration and multi-year ice fraction are used in this comparison.