The MODIS/ASTER airborne simulator (MASTER) Ð a new instrument for earth science studies Simon J. Hook a, *, Jeffrey J. Myers b , Kurtis J. Thome c , Michael Fitzgerald b , Anne B. Kahle a a Mail Stop 183-501, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91009, USA b SAIC, NASA Ames Research Center, Moffett Field, CA 94035, USA c Optical Sciences Center, University of Arizona, Tucson, AZ 85721, USA Received 25 October 1999; accepted 23 July 2000 Abstract The MODIS/ASTER Airborne Simulator was developed for the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Moderate Resolution Imaging Spectroradiometer (MODIS) projects. ASTER and MODIS are both spaceborne imaging instruments on the Terra platform launched in the fall of 1999. Currently MASTER is flown on the Department of Energy (DOE) King Air Beachcraft B200 aircraft and the NASA DC-8. In order to validate the in-flight performance of the instrument, the Jet Propulsion Laboratory and the University of Arizona conducted a joint experiment in December 1998. The experiment involved overflights of the MASTER instrument at two sites at three elevations (2000, 4000, and 6000 m). The two sites: Ivanpah Playa, California, and Lake Mead, Nevada, were selected to validate the visible ±shortwave infrared and thermal infrared (TIR) channels, respectively. At Ivanpah Playa, a spectrometer was used to determine the surface reflectance and a sun photometer used to obtain the optical depth. At Lake Mead contact and radiometric surface lake temperatures were measured by buoy-mounted thermistors and self-calibrating radiometers, respectively. Atmospheric profiles of temperature, pressure, and relative humidity were obtained by launching an atmospheric sounding balloon. The measured surface radiances were then propagated to the at-sensor radiance using radiative transfer models driven by the local atmospheric data. There was excellent agreement between the predicted radiance at sensor and the measured radiance at sensor at all three altitudes. The percent difference between the channels not strongly affected by the atmosphere in the visible ± shortwave infrared was typically 1 ± 5% and the percent difference between the TIR channels not strongly affected by the atmosphere was typically less than 0.5%. These results indicate the MASTER instrument should provide a well-calibrated instrument for Earth Science Studies. It should prove particularly valuable for those studies that leverage information across the electromagnetic spectrum from the visible to the TIR. D 2001 Elsevier Science Inc. All rights reserved. 1. Introduction The MODIS/ASTER Airborne Simulator (MASTER) was developed to support scientific studies by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Moderate Resolution Imaging Spectroradi- ometer (MODIS) projects. ASTER and MODIS (Barnes, Pagano, & Salomonson, 1998; Salomonson, Barnes, May- mon, Montgomery, & Ostrow, 1989; Yamaguchi, Kahle, Tsu, Kawakami, & Pniel, 1998) are both spaceborne ima- ging instruments on the first Earth Observing System plat- form launched in the fall of 1999. The characteristics of these instruments are summarized in Table 1 and the characteristics of the MASTER instrument are summarized in Table 2. The primary mission of MASTER is to: Collect ASTER-like and MODIS-like data sets to support the validation of the ASTER and MODIS geophysical retrieval algorithms. Collect these data sets at a higher spatial resolution than the spaceborne datasets to permit scaling studies and comparisons with in-situ measurements. Underfly the Terra ASTER and MODIS sensors to provide an additional radiometric calibration to assist with satellite instrument performance characterization. This is particularly important for ASTER where on-board calibra- tion is dependent on a single blackbody in the thermal infrared (TIR) and only partial aperture illumination in the visible±near infrared (VNIR). * Corresponding author. E-mail address: simon.j.hook@jpl.nasa.gov (S.J. Hook). www.elsevier.com/locate/rse Remote Sensing of Environment 76 (2001) 93 ± 102 0034-4257/00/$ ± see front matter D 2001 Elsevier Science Inc. All rights reserved. PII:S0034-4257(00)00195-4