NASA - SatCORPS - AVHRR-CDR

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AVHRR CDR

AVHRR CDR

Overview

One of the most pressing climate issues identified by the IPCC's Fourth Assessment is the need for a long-term analysis of cloud properties to better understand the impact of cloud and aerosol radiative forcing on various aspects of climate, especially surface temperature and its diurnal variation. Cloud and aerosol radiative forcing are linked by the indirect effects of aerosols on the the microphysical properties of clouds and the subsequent impact on the radiative absorption of those clouds. To understand radiative forcing over long time periods, it is necessary to measure cloud and aerosol properties over the globe using a consistent set of proven algorithms applied to a long-term record of consistently calibrated and quality- controlled satellite imager data. Knowing how clouds vary with climate change and how well climate models reproduce such variability through modeled feedbacks is critical to understanding how well the models can predict climate. In a complementary fashion, it is also essential to monitor the changes in Earth surface properties when clouds are not present. A fundamental parameter is clear-sky radiance, which can be used to determine a variety of surface properties including land or sea surface skin temperature, surface spectral albedo, and vegetation index. Relating those properties and surface air temperature to changes in vegetation and urbanization is another important component of understanding climate change.

As part of the NOAA NCDC Climate Data Record (CDR) program, the NASA Langley Cloud and Radiation Research group (PI: Dr. Patrick Minnis) is currently developing a Thematic CDR (TCDR) consisting of cloud amount, phase, optical depth, effective particle size, height, and temperature extending back to 1978 using data from the AVHRR instrument. The TCDR will be consistent with CERES MODIS cloud properties, though some modifications to these algorithms will be required to operate on the 5- channel and lower spatial resolution AVHRR Global Area Coverage (GAC) data. The CERES MODIS cloud property retrieval algorithm has a reliable 10-year data record and will continue to operate with NPP VIIRS.

In addition to having a suite of mature, robust cloud and clear-sky analysis algorithms, it is essential that the satellite data are properly calibrated to produce reliable cloud and clear sky properties. Detection of small climate trends requires high accuracy in the initial radiance. An addition component of this NOAA NCDC CDR effort is the development of a Fundamental CDR (FCDR) consisting of a calibration record of visible (0.65 micrometer) and near-infrared (0.87 and 1.6 micrometers) channels for: 1) AVHRR instruments on NOAA-5 through NOAA-18 and MetOp-A, 2) US geostationary (GEO) imagers for SMS-1 through GOES-13, and 3) Non-US GEO imagers such as GMS, Meteosat, MTSAT, FY-2, and Kalpana after 1982. Stable and accurate visible channel calibration is ensured through matching modern AVHRR and GEO data with that of Aqua MODIS using the Nearly Simultaneous Ray- matched Technique and the Deep Convective Cloud Technique. These calibrations are then transferred back in time through the use of time- overlapping LEO and GEO data.

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The Dryden Flight Research Center (DFRC) is NASA's center for aeronautical flight research and atmospheric flight operations. DFRC is chartered to research, develop, verify, and transfer advanced aeronautics, space and related technologies. It also serves as a backup landing site for the Space Shuttle and a facility to test and validate design concepts and systems used in development and operation of the Orbiters.

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