Confidence in Calibration Using UV-VIS-NIR Spectroradiometers
Calibration produces trusted data based on traceability to standards, awareness of measurement uncertainties, verification and validation. Calibration characterizes the parameters needed to understand and describe a sensor’s performance. Radiometric calibration identifies and quantifies a sensor’s response to a known radiometric input. The most common lab input comes from an integrating sphere. For best practice an audit trail for calibrations is necessary from standards to an integrating sphere to a satellite sensor in space. To achieve this goal, scientists and engineers start with NIST-traceable radiometric calibration standards. As satellite sensors improve in precision and accuracy, the need for rigorous pre-launch calibration becomes increasingly important. A series of detailed calibrations are used to fully characterize satellite sensors’ wavelength scale, spectral response functions, pointing sensitivity, radiometric accuracy and other key parameters.
Integrating spheres show very uniform radiance distribution and are used in a range of applications for the testing and calibration of imaging and non-imaging systems such as focal plane arrays and cameras. They may be used to perform pixel gain normalization, photographic sensitometry, remote observation system calibration, and the test and calibration of instruments for multi-spectral and hyperspectral imaging. To ensure traceability back to standards, integrating spheres need periodic calibration. Typically, shipment back to a vendor’s lab is rarely practical and scientists require a way to calibrate at their location. That location is usually a room where a large sphere using high wattage FELS lamps can create ambient heat. For some spectroradiometers and radiometers, the heat can cause the silicon arrays used to overheat, giving uncertain results in the UV-VIS wavelengths.
An ideal transfer standard, according to NIST, would have uniform and smooth power distribution with high correlated color temperature across the intended spectral range, low aging rate, uniform spatial intensity distribution, and good reproducibility. To meet the needs of integrating sphere owners who have system lamps with high operating hours, light sources more than two years old, a mandate for annual calibration, or systems too large to send out for calibration, the CalibraSpec™ 4500A and CalibraSpec™ 6500A spectroradiometers from Spectral Evolution with their state of the art cooling and stability technology offer the best functionality for on-site calibration and deliver stable performance without drift across a range of ambient temperatures.
Lightweight and portable, The CalibraSpec 4500A and CalibraSpec 6500A provide the ultimate in high performance and measurement stability across a wide range of ambient temperatures and environments. The CalibraSpec 4500A and CalibraSpec 6500A’s measurement stability eliminates variability between various integrating spheres and retains NIST traceability. The CalibraSpec 4500A and CalibraSpec 6500A include three thermoelectrically cooled photodiode arrays and have been built to meet the needs of our customers such as NIST and NASA.
