Abstract
The Landsat-8 Operational Land Imager (OLI) was radiometrically calibrated prior to launch in terms of spectral radiance, using an integrating sphere source traceable to National Institute of Standards and Technology (NIST) standards of spectral irradiance. It was calibrated on-orbit in terms of reflectance using diffusers characterized prior to launch using NIST traceable standards. The radiance calibration was performed with an uncertainty of ~3%; the reflectance calibration to an uncertainty of ~2%. On-orbit, multiple calibration techniques indicate that the sensor has been stable to better than 0.3% to date, with the exception of the shortest wavelength band, which has degraded about 1.0%. A transfer to orbit experiment conducted using the OLI’s heliostat-illuminated diffuser suggests that some bands increased in sensitivity on transition to orbit by as much as 5%, with an uncertainty of ~2.5%. On-orbit comparisons to other instruments and vicarious calibration techniques show the radiance (without a transfer to orbit adjustment), and reflectance calibrations generally agree with other instruments and ground measurements to within the uncertainties. Calibration coefficients are provided with the data products to convert to either radiance or reflectance units.
Highlights
Landsat-8 was launched on 11 February 2013 with two Earth imaging sensors on-board: The Operational Land Imager (OLI) that will be discussed in this paper and the Thermal Infrared Sensor (TIRS)
The OLI responsivities were derived by dividing the net linearized OLI response by the OLI relative spectral weighted radiances of the Death Star Source (DSS) Level 10 (Figure 12). These pre-launch gains were the initial gains stored in the Calibration Parameter File (CPF) for use by the Landsat Product Generation System (LPGS); the gain values provided in the CPF are contained in two fields: OLI_ABSOLUTE_GAINS, which are averages for each focal plane module and OLI_RELATIVE_GAINS, which are individual detector values referenced to each Focal Plane Modules (FPMs) average
(3) All bands gains were adjusted to correct for an outdated radiance file that was mistakenly used in the pre-launch calibration data reduction for all bands; this decreased the radiance in all bands by ~2%, without changing the reflectance calibration
Summary
Landsat-8 was launched on 11 February 2013 with two Earth imaging sensors on-board: The Operational Land Imager (OLI) that will be discussed in this paper and the Thermal Infrared Sensor (TIRS). Key among the considerations in the design, build, test and operation of the OLI and the Landsat-8 system is providing data to the user community that is well understood and accurately referenced to standards of radiance (±5%, 1 sigma or k = 1) and reflectance (±3%, k = 1) These accuracies are achieved with a combination of factors including: (1) precision temperature control for the focal plane and focal plane electronics; (2) state of the art contamination control for all the optical surfaces, including the solar diffusers; (3) rigorous maintenance and validation of the radiance and reflectance scales as transferred from the national laboratories to the instrument and calibration devices; (4) a precisely maneuverable spacecraft to allow calibration using the sun and moon; (5) a concept of operations that includes. Aspects of the material included in this paper have been presented at a number of conferences [4,5,6,7,8,9,10,11]
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