Pahlevan, N; Raqueno, NG; Schott, JR (2012). Cross-Calibration of Landsat-7's Visible-Near-Infrared Bands with Terra-MODIS over Dark Waters. OCEAN SENSING AND MONITORING IV, 8372, 837210.
Since its launch, the Enhanced Thematic Mapper plus (ETM+) onboard Landsat-7 has been continuously monitored via different calibration techniques to ensure it maintains the science requirements for the demanding application areas. The majority of its applications, including agriculture and forestry, require a robust calibration for medium to high reflective targets. However, when imaging water resources, then the question becomes whether the calibration coefficients are valid for the dark end of the sensor's responsivity curve. Motivated by the Landsat Data Continuity Mission (LDCM) and its potential for providing long-term, robust water studies, in this effort, the calibration status of Landsat-7's visible bands are examined using a cross-calibration technique. The well-calibrated Terra-MODIS scenes of the past decade over relatively optically stable waters were chosen to evaluate Landsat-7's stability. Following the geo-registration, homogenous areas exhibiting near, identical atmospheric conditions were specified as regions of interest in the calibration sites representing a broad range of water-leaving signals. The differences in the relative spectral response functions of the two sensors were accounted for via a model-based technique. The cross-comparison showed that the calibration instability of Landsat-7's reflective bands lie well within its radiometric uncertainty. The slight calibration differences were found to be less than 1%, 0.5%, and 2.5% for the blue, green and the red bands obtained for the period when the Terra-MODIS has been radiometrically stable. The Landsat-7's NIR band, however, exhibits, on average, 6.3% higher signals than those of Terra-MODIS. The results indicate that although Landsat-7 is well calibrated, its calibration status should be quantified rigorously for water studies when physics-based methods are employed for the removal of atmospheric effects. The over-water characterization of Landsat satellites becomes more crucial when the LDCM becomes operational.