Laboratory calibration

Laboratory calibration of the HySpex instrument includes determining radiometric calibration coefficients (to enable conversion of DN values to radiance and ultimately reflectance) as well as the dark signal, pixel responsivity / non-uniformity, band wavelength central positions, and the field of view (FOV) of each pixel. Further laboratory characterizations of the instrument provide additional information on the systems performance such as sensor linearity, SNR, dynamic range, stray light, spectral/spatial resolution and mis-registrations.

We relied on the instrument provider (NEO) of our Hyspex system for instrument calibration and to provide calibration coefficients using equipment traceable to NIST-equivalent European standards. We also have the NEON Sensor Test Facility, that can provide calibration traceable to NIST standards within the United States.

Now, HyLab works with UAFs optical sensor calibration lab (run by Co-PI Don Hampton) to monitor the stability of the manufacturer and NEON supplied calibration parameters using a complete calibrated Spherical Integrating Source (SIS) set (see photo on the left). Besides the bench-top, 300 mm diameter, barium-sulfate coated SIS with a 127 mm diameter port window, the set includes a 100W quartz halogen light source, a 4-channel optometer, and pencil style calibration lamps for various gas emission lines.

For field vicarious calibrations, concurrent with each airborne data acquisition missions, we set up a temporary meteorological station that records atmospheric temperature, humidity, wind speed and direction, and incoming and outgoing solar radiations. For teh first test flight near Fairbanks, we also use field-portable Microtops II Sunphotometer with a nearby Cimel sun photometer located at the Bonanza Creek AERONET (AErosol RObotic NETwork) site to record aerosol optical thickness (AOT) and column water vapor. Additionally, we used a Fieldspec Pro for target reflectance measurement of well-characterized ground targets in the Fairbanks area.