Calibration of GOES Using Satellite and ARESE Aircraft Data J. K. Ayers, D. R. Doelling, L. Nguyen, W. L. Smith, Jr. Analytical Services and Materials, Inc. Hampton, Virginia P. Minnis Atmospheric Sciences Division NASA Langley Research Center Hampton, Virginia Introduction The Geostationary Operational Environmental Satellite (GOES) data are a key component of the Atmospheric Radiation Measurement (ARM) Program. They complement the suite of surface measurements taken at the ARM sites in Oklahoma. The data are used to derive cloud properties and the top-of-the- atmosphere radiation budget at several time and space scales. Calibration of the GOES narrowband visible (0.65 μm) and infrared (11 μm) radiances is essential for accurate determination of quantities such as cloud optical depth, height, and emittance. Conversion of these radiances to broadband shortwave albedo and longwave flux is performed using empirical functions based on coincident Earth Radiation Budget Satellite (ERBS) measurements taken prior to the ARM program. These calibrations and conversions are based on historical matched satellite-to-satellite datasets. It is important to have an independent verification of these calibrations. A contemporaneous calibration using a reliable source is even better. The ARM/UAV (Unmanned Aerospace Vehicle) Program includes well-calibrated airborne radiance and flux measurements that can be used to verify and improve the calibration coefficients for operational meteorological satellites. This paper uses satellite and aircraft measurements taken during the 1995 ARM Enhanced Shortwave Experiment to perform calibrations of the GOES-8 visible and infrared sensors. Satellite Data The ARM Enhanced Shortwave Experiment (ARESE) was conducted over the ARM Southern Great Plains site in northern Oklahoma from September 25 - November 1, 1995. Visible (VIS) and infrared (IR) radiances were observed every 15 min by the GOES-8 (G8) and GOES-9 (G9) satellites. G8 was located over the equator at 75°W, while G9 was centered at 90°W. The nominal resolutions of the VIS and IR sensors are 1 and 4-km , respectively. The pre- launch gain for the G8 VIS calibration was adjusted shortly after launch to yield L 8 = 0.606 D 8 - 14.33, where D is the 10-bit digital count and L 8 is the G8 radiance in Wm -2 sr -1 μm -1 . The G9 VIS radiance L 9 was determined by correlating average values of G9 VIS counts D 9 with collocated values of D 8 at local noon along the longitude (82.5°W) bisecting the two satellites (Fig. 1). The resulting calibration is L 9 = 0.556 D 9 - 15.37. 0 100 200 300 400 500 600 0 100 200 300 400 500 600 GOES-9 VISIBLE COUNT GOES-8 VISIBLE COUNT Fig. 1. Correlation of matched GOES-8 and GOES-9 visible counts taken at 82.5°W, 1730 UTC, September 12, 1995.