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Ocean PHILLS hyperspectral imager: design, characterization, and calibration

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Abstract

The Ocean Portable Hyperspectral Imager for Low-Light Spectroscopy (Ocean PHILLS) is a hyperspectral imager specifically designed for imaging the coastal ocean. It uses a thinned, backside-illuminated CCD for high sensitivity and an all-reflective spectrograph with a convex grating in an Offner configuration to produce a nearly distortion-free image. The sensor, which was constructed entirely from commercially available components, has been successfully deployed during several oceanographic experiments in 1999–2001. Here we describe the instrument design and present the results of laboratory characterization and calibration. We also present examples of remote-sensing reflectance data obtained from the LEO-15 site in New Jersey that agrees well with ground-truth measurements.

©2002 Optical Society of America

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Figures (8)

Figure 1.
Figure 1. Design and specifications for the HyperSpecTM VS-15 Offner Spectrograph.
Figure 2.
Figure 2. Spatial image of the bar target showing 1024 spatial channels (horizontal) and 128 (512 binned by 4) spectral channels (vertical dimension). The non-uniformity from the top to the bottom is due to the spectral properties of the light source which is blue rich and has spectral emission lines.
Figure 3.
Figure 3. The spectral response of the PHILLS to 594.1 nm Helium-Neon laser light. The data are unbinned with a channel width of 1.15 nm. The inset figure is a close-up view for channels near the spectral peak plotted on a logarithmic scale.
Figure 4.
Figure 4. Image of a low pressure Mercury lamp showing 1024 spatial channels (horizontal) by 512 spectral channels (vertical dimension).
Figure 5.
Figure 5. a) Linear fits to Ocean PHILLS radiometric calibration data for four selected wavelengths. b) Typical values of the radiometric calibration gain for the left (sample 488, top curve) and right (sample 517, bottom curve) side of the 1024 sample CCD. The spectral channels that correspond to the response curves shown in Figure 5a are marked with their legend labels.
Figure 6.
Figure 6. Typical at-sensor PHILLS radiance spectra and corresponding signal-to-noise ratios for bin-by-4 data from the LEO-15 site: (a) coastal water, (b) vegetated land.
Figure 7.
Figure 7. PHILLS image from the 2001 LEO-15 deployment (39 31 05 N and 74 20 47 W, 14:18 GMT, 31 July 2001.)
Figure 8:
Figure 8: Atmospherically-corrected remote-sensing reflectance spectrum from the pixel indicated with an X in Figure 7 compared with a ground-truth measurement obtained with a hand-held radiometer at the site.

Tables (1)

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Table 1. Measured spatial performance metrics for the complete PHILLS, including lens, spectrograph, and camera.

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