Abstract
Laser-based laboratory calibrations in the facility for Spectral Irradiance and Radiance responsivity Calibrations using Uniform Sources (SIRCUS) of the National Institute of Standards and Technology (NIST) have achieved detector calibration with uncertainties less than 0.1 % in the silicon spectral region. Because of the high power of lasers, there is also a drastic increase in dynamic range covering more than 5 orders of magnitude. The low measurement uncertainty and high dynamic range allow accurate assessment of out-of-band performance for flight instruments such as the Suomi National Polar-orbiting Partnership (NPP) Visible and Infrared Imager Radiometer Suite (VIIRS) sensor which was calibrated in 2010 for Absolute Spectral Responsivity (ASR) with full aperture illumination using a tunable laser and a large integrating sphere with an approximately 0.5% uncertainty in radiance responsivity.
With the calibration data, it is now possible to fully evaluate the effect of out-of-band (OOB) contribution on at-sensor water-leaving radiance and derive strategy to alleviate variations from OOB scattering and reduce data product uncertainties. In this work, we present a sensitivity analysis of the Top-of-Atmosphere (TOA) measurement for varying chlorophyll concentrations and column water vapor based on measured detector Relative Spectral Responsivity (RSR). A conventional band-averaged radiance approach is taken and histograms are presented for different bands of radiometers to illustrate the data uncertainty from these variations as well as the global seasonal differences. We show how conventional lamp calibration at ground and on board solar calibration resulted in large deviation from OOB scattering because of mismatch with ocean color spectra. We will also present similar analysis for the detectors of the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS).
A Study of Out-of-band Uncertainties for On-orbit Ocean Color Measurements Based on Laser Calibration of Flight Radiometers
Laser-based laboratory calibrations in the facility for Spectral Irradiance and Radiance responsivity Calibrations using Uniform Sources (SIRCUS) of the National Institute of Standards and Technology (NIST) have achieved detector calibration with uncertainties less than 0.1 % in the silicon spectral region. Because of the high power of lasers, there is also a drastic increase in dynamic range covering more than 5 orders of magnitude. The low measurement uncertainty and high dynamic range allow accurate assessment of out-of-band performance for flight instruments such as the Suomi National Polar-orbiting Partnership (NPP) Visible and Infrared Imager Radiometer Suite (VIIRS) sensor which was calibrated in 2010 for Absolute Spectral Responsivity (ASR) with full aperture illumination using a tunable laser and a large integrating sphere with an approximately 0.5% uncertainty in radiance responsivity.
With the calibration data, it is now possible to fully evaluate the effect of out-of-band (OOB) contribution on at-sensor water-leaving radiance and derive strategy to alleviate variations from OOB scattering and reduce data product uncertainties. In this work, we present a sensitivity analysis of the Top-of-Atmosphere (TOA) measurement for varying chlorophyll concentrations and column water vapor based on measured detector Relative Spectral Responsivity (RSR). A conventional band-averaged radiance approach is taken and histograms are presented for different bands of radiometers to illustrate the data uncertainty from these variations as well as the global seasonal differences. We show how conventional lamp calibration at ground and on board solar calibration resulted in large deviation from OOB scattering because of mismatch with ocean color spectra. We will also present similar analysis for the detectors of the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS).