DOI: 10.5281/zenodo.3048419
title: AIRBORNE SPECTROMETER MEASUREMENTS FMOM BOREAL SNOW-COVERED LANDSCAPE

description: The dataset contains 10 meter resolution reflectance data from boreal snow-covered landscape. The purpose of the airborne measurements was to investigate the effect of forest canopy on optical remote sensing signals for snow-covered surfaces. The hyperspectral airborne data was acquired with an AisaDUAL imaging spectrometer on March 18 and on March 21, 2010 in Sodankylä, Finland. The image swath was 240 meters and flight lines were several kilometers long. The original spatial resolution of the data is 80 cm x 80 cm, but it was resampled to pixel size of 10 m x 10 m. All measurements were carried out in non-cloudy conditions (0/8 to 2/8 cloud cover). On 18 March, the tree canopy was snow-free and snow on the ground was several days old, while on 21 March, the tree canopy was snow-covered and snow on ground was fresh. The data contains mosaics of the flight lines for the bands 555 nm, 645 nm, 858.5 nm and 1640 nm for both days 18 March 2010 and 21 March 2010.
description: Sampling: The airborne hyperspectral data was acquired with an AisaDUAL imaging spectrometer manufactured by Spectral Imaging Ltd (SPECIM). The airborne spectral measurements were made from helicopter at an altitude of 800 m producing a spatial resolution of 0.8 m and swath of 240 m. The flight lines were several kilometers long. All measurements were carried out in direct illumination (i.e. clear sky: 0/8 to 2/8 cloud cover). The Oxford Technical Solutions RT4000 GPS/INS was utilized to enable high accuracy measurements with low drift rates. The instrument foreoptics unit was set to look at nadir (0 degrees) direction and the field of view (FOV) was 17 degrees. Processing: The AisaDUAL spectrometer data was radiometrically and geometrically corrected by using CaliGeo tool by SPECIM in the ENVI software by Bestcomp 97. Kft. The original spectral resolution for the VNIR bands was 5 nm and for SWIR bands 6 nm totaling to 359 spectral bands. Airborne radiances were calibrated by comparing them to concurrent radiances measured from 30 meter high mast from forest site and determining calibration coefficients to airborne data by using least squares fitting technique. The original spatial resolution of the data is 80 cm x 80 cm. From this data the bands 555 nm, 645 nm, 858.5 nm and 1640 nm were extracted from the spectra by using the band specific FWHM criterion (Full width at half maximum) corresponding to MODIS bands. For these bands the data was filtered with mean filter using 12x12 window corresponding to pixel size of 10 metre. Reflectances were calculated by using simultaneously measured radiance from a white Spectralon panel at a particular wavelength to describe incoming radiation. Spectralon measurements were done with a well calibrated spectrometer installed on 30 m high mast. The utilized instrument of the mast was Field Spec Pro JR from Analytical Spectral Devices Inc (ASD).
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