Evaluation of Long-Term Calibrations of the AVHRR Visible Radiances

Abstract

Two systematic calibrations have been compiled for the visible radiances measured by the series of AVHRR instruments flown on the NOAA operational polar weather satellites: one by the International Satellite Cloud Climatology Project (ISCCP), anchored on NASA ER-2 underflights in the 1980s and early 1990s and covering the period 1981-2009, and one by the PATMOS-x project, anchored on comparisons to the MODIS instruments on the Aqua and Terra satellites in the 2000s and covering the period 1979-2010 (this result also includes calibration for the near-IR channels). Both methods have had to extend their anchor calibrations over a long series of instruments using different vicarious approaches, so a comparison provides an opportunity to evaluate how well this extension works by cross-checking the results at the anchor points. The basic result of this comparison is that for the ''afternoon'' series of AVHRRs, the calibrations agree to within their mutual uncertainties. However, this retrospective evaluation also shows that the representation of the time variations can be simplified. The ISCCP procedure had much more difficulty extending the calibration to the ''morning'' series of AVHRRs with the calibrations for NOAA-15 and NOAA-17 exceeding the estimated uncertainties. Given the general agreement, a new calibration for all AVHRR visible radiances (except TIROS-N, NOAA-6, NOAA-19, and MetOp-A) is proposed that is based on the average of the best linear fits to the two time records. The estimated uncertainty of these calibrations is 63% absolute (scaled radiance units).

The International Satellite Cloud Climatology Project H-Series climate data record product

“…The combination of the geostationary and polar-orbiting satellites allows ISCCP to establish an intercalibration procedure in which radiances from imagers onboard the geostationary satellites are normalized to the low-earth-orbit AVHRR radiances from the afternoon polar orbiter satellite series. In this approach, NOAA-9 acts as the absolute reference through 2009 (Rossow and Ferrier, 2015). As the H-series dataset is processed forward in time, NOAA-18 will serve this function.…”

“…Results of the space-time tests are used in conjunction with the ancillary products to obtain a global composite of clear-sky radiances for each image pixel location and time (CLRSKY). Second, cloudy conditions are diagnosed when IR-or VIS-observed satellite radiances sufficiently deviate from estimated values using various combinations of VIS and IR thresholds (BX) (Rossow and Garder, 1993a, b;. From here, the composite clear-sky radiances are revised based on the prior detection threshold results and application of revised threshold tests of each image's pixels against the revised composite clear-sky radiance values using the ancillary products (CY).…”

“…Although a correction is applied for the AVHRR NOAA KLM calibration error, most calibration issues present in ISCCP D are also present in the H-series product. Users may refer to Brest and Rossow (1992), Desormeaux et al (1993), Brest et al (1997), Inamdar and Knapp (2015), and Rossow and Ferrier (2015). All these citations, plus many others, are given in the Climate Algorithm Theoretical Basis Document (C-ATBD).…”

“…ISCCP ten most cited papers that have contributed to the dataset's more than 15 000 citations. The number of citations given here is based on Google Analytics, accessed February 10, 2017. ies have evaluated the product to highlight specific opportunities to advance the dataset (Rossow and Ferrier, 2015;Evan et al, 2007;Norris, 2000;Rossow and Schiffer, 1999;Stubenrauch et al, 2013) and take further advantage of its record, spanning over 25 years, to improve its capability to estimate long-term trends in global cloudiness. This detail is relevant considering newer cloud datasets that have shorter records but improved capabilities for cloud detection and retrieval due to technological advancements that include active spaceborne sensors (e.g., Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations -CALIPSO -and CloudSat) and cloud datasets that rely on newer passive imagers with higher spectral, spatial, radiometric, and temporal resolutions (Platnick et al, 2003;Hutchison et al, 2005;Stengel et al, 2017).…”

The International Satellite Cloud Climatology Project H-Series Climate Data Record Product

“…In this approach, NOAA-9 acts as the absolute reference through 2009 89 (Rossow and Ferrier, 2015). NOAA-18 now performs this function for 2010 and beyond.…”