Preservation Content Specification (PCS): 3.4.2: Calibration Data Traceability
Calibration data for ASTER includes time-dependent radiometric calibration coefficients (RCCs), associated degradation curves, geometric calibration parameters, instrument and platform engineering telemetry, and supporting calibration inputs such as lookup tables (LUTs) and ancillary datasets used during processing. These data are used to account for instrument performance changes and to support geometric and radiometric accuracy over the mission lifetime and are maintained separately from Level-0 and Level-1 products.
Radiometric and geometric calibration parameters are maintained within online calibration database files that are updated throughout the mission via calibration and validation activities, including onboard calibration, vicarious calibration, and image-based analysis.
Early RCC versions (V1–V3) were derived primarily from onboard calibrator measurements; however, inconsistencies identified through vicarious and cross-calibration approaches led to subsequent updates. RCC Version 4 incorporated combined calibration approaches, while RCC Version 5 was derived using vicarious and lunar calibration methods, resulting in improved inter-band consistency and traceability.
These calibration updates were implemented through processing system updates (e.g., Product Generation Executable [PGE] changes) and propagated through Level-1 and higher-level data products. In operational products, radiometric calibration is tracked through radiometric database versions (e.g., RADIOMETRICDBVERSION), which are recorded in product metadata and provide traceability to the calibration coefficients applied during processing.
Geometric calibration data include parameters and supporting datasets used to determine the spatial location and alignment of observations. These include geometric correction database elements such as detector line-of-sight vectors, pointing axis information, and conversion coefficients, as well as geolocation data expressed in latitude and longitude for each scene. These parameters are initially derived from preflight calibration activities and are refined through post-launch validation using ground control points (GCPs) and image matching techniques.
Geometric calibration updates are maintained through geometric correction database versions (e.g., GEOMETRICDBVERSION), which are captured in product metadata. Unlike radiometric calibration coefficients, geometric calibration parameters are not typically referenced through a formal, widely used version series (e.g., RCC V1–V5); instead, their traceability is captured through database versions and processing history.
Additional calibration data include instrument and platform telemetry (e.g., detector response, instrument temperatures), spacecraft attitude and ephemeris information, and mission event records. These inputs provide context for both radiometric and geometric calibration and are used to assess data quality and support calibration adjustments. Acquisition logs and processing records are also used to identify data gaps and anomalies that may impact calibration.
Together, these calibration data components support the application and maintenance of calibration throughout the mission lifetime and enable traceability of how calibration inputs influence data product generation. Supporting calibration studies, geometric correction databases, and release documentation are maintained by the ASTER Science Team and associated processing systems.