Abstract
An initial validation of the Along Track Scanning Radiometer (ATSR) Reprocessing for Climate (ARC) retrievals of sea surface temperature (SST) is presented. ATSR-2 and Advanced ATSR (AATSR) SST estimates are compared to drifting buoy and moored buoy observations over the period 1995 to 2008. The primary ATSR estimates are of skin SST, whereas buoys measure SST below the surface. Adjustment is therefore made for the skin effect, for diurnal stratification and for differences in buoy–satellite observation time. With such adjustments, satellite-in situ differences are consistent between day and night within ~0.01K. Satellite-in situ differences are correlated with differences in observation time, because of the diurnal warming and cooling of the ocean. The data are used to verify the average behaviour of physical and empirical models of the warming/cooling rates.Systematic differences between adjusted AATSR and in-situ SSTs against latitude, total column water vapour (TCWV), and wind speed are less than 0.1K, for all except the most extreme cases (TCWV <5kgm–2, TCWV >60kgm–2). For all types of retrieval except the nadir-only two-channel (N2), regional biases are less than 0.1K for 80% of the ocean. Global comparison against drifting buoys shows night time dual-view two-channel (D2) SSTs are warm by 0.06±0.23K and dual-view three-channel (D3) SSTs are warm by 0.06±0.21K (day-time D2: 0.07±0.23K). Nadir-only results are N2: 0.03±0.33K and N3: 0.03±0.19K showing the improved inter-algorithm consistency to ~0.02K. This represents a marked improvement from the existing operational retrieval algorithms for which inter-algorithm inconsistency is >0.5K. Comparison against tropical moored buoys, which are more accurate than drifting buoys, gives lower error estimates (N3: 0.02±0.13K, D2: 0.03±0.18K). Comparable results are obtained for ATSR-2, except that the ATSR-2 SSTs are around 0.1K warm compared to AATSR.
Highlights
A new sea surface temperature (SST) retrieval has been developed for the Along Track Scanning Radiometer (ATSR) instruments, with a view to developing an independent SST time-series for climate applications (Merchant et al, 2008a)
This paper presents an initial comparison of the new satellitederived SST estimates obtained for ATSR-2 and Advanced ATSR (AATSR) with independent measurements
Radiometers operating at infrared wavelengths, such as the ATSR instruments, are sensitive to radiation emitted from the layer between the air–sea interface and about 20 μm below the air–sea interface, depending on wavelength
Summary
A new sea surface temperature (SST) retrieval has been developed for the Along Track Scanning Radiometer (ATSR) instruments, with a view to developing an independent SST time-series for climate applications (Merchant et al, 2008a). We derive time-adjusted depth SSTs (estimates adjusted for the ocean thermal skin effect, near-surface stratification and differences in observation time). The latter are intended to be more directly comparable to the in situ data used for validation. The main purpose of the paper is the initial validation of new SSTs obtained within the ATSR Reprocessing for Climate project (ARC) (Merchant et al, 2008a). Homogenisation will be a crucial step in developing a record appropriate for climate, and will be reported in a subsequent article
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