Abstract
Standard oceanographic processing of the visible infrared imaging radiometer suite (VIIRS) and the moderate resolution imaging spectroradiometer (MODIS) data uses established atmospheric correction approaches to generate normalized water-leaving radiances ( nLw ) and bio-optical products. In many cases, there are minimal differences between temporally and spatially coincident MODIS and VIIRS bio-optical products. However, due to factors such as atmospheric effects, sensor, and solar geometry differences, there are cases where the sensors’ derived products do not compare favorably. When these cases occur, selected nLw values from one sensor can be used to vicariously calibrate the other sensor. Coincident VIIRS and MODIS scenes were used to test this cross-sensor calibration method. The VIIRS sensor was selected as the “base” sensor providing “synthetic” in situ nLw data for vicarious calibration, which computed new sensor gain factors used to reprocess the coincident MODIS scene. This reduced the differences between the VIIRS and MODIS bio-optical measurement. Chlorophyll products from standard and cross-sensor calibrated MODIS scenes were fused with the VIIRS chlorophyll product to demonstrate the ability for this cross-sensor calibration and product fusion method to remove atmospheric and cloud features. This cross-sensor calibration method can be extended to other current and future sensors.
Highlights
The moderate resolution imaging spectroradiometer (MODIS) on the Terra satellite has been operational since 1999, and the MODIS sensor on the Aqua satellite since 2002.1 The visible infrared imaging radiometer suite (VIIRS) on the Suomi National Polar-orbiting Partnership (SNPP) satellite was launched in 2012.2 VIIRS is continuing the legacy of earth and ocean observations established by MODIS, the sea-viewing wide-field-of-view sensor (SeaWiFS),[3] and the coastal zone color scanner.[4]
A cross-sensor calibration methodology using a vicarious calibration methodology was applied to Mississippi Bight and Chesapeake Bay VIIRS and MODIS scene pairs
Estimates of normalized water-leaving radiances (nLw) from the VIIRS scene at 20 points for each scene pair were used as synthetic in situ nLw data for the cross-calibration of the MODIS scene. This generated cross-calibrated gains factors for the MODIS data which when applied to the MODIS Lt data produced derived nLw values that were in better agreement with the VIIRS derived nLw values
Summary
The moderate resolution imaging spectroradiometer (MODIS) on the Terra satellite has been operational since 1999, and the MODIS sensor on the Aqua satellite since 2002.1 The visible infrared imaging radiometer suite (VIIRS) on the Suomi National Polar-orbiting Partnership (SNPP) satellite was launched in 2012.2 VIIRS is continuing the legacy of earth and ocean observations established by MODIS, the sea-viewing wide-field-of-view sensor (SeaWiFS),[3] and the coastal zone color scanner.[4]For satellite-based earth observing sensors, accurate radiometric measurements are required to correctly derive in-water ocean properties. Laboratory radiometric calibration performed prior to launch enables the sensor-measured digital counts to be converted into radiance units. After launch these sensors provide total radiance (Lt) measurements at the top of the atmosphere. Because the Lt over the ocean is dominated by atmospheric radiances and the radiances from the ocean are low, relative to radiances from land targets, accurate atmospheric correction is required to derive water-leaving radiance (Lw) from the Lt values. These Lw values are normalized using the solar zenith angle, diffuse transmittance, bi-directional reflectance
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