The Potential of Autonomous Ship-Borne Hyperspectral Radiometers for the Validation of Ocean Color Radiometry Data

Abstract

Calibration and validation of satellite observations are essential and on-going tasks to ensure compliance with mission accuracy requirements. An automated above water hyperspectral radiometer significantly augmented Australia's ability to contribute to global and regional ocean color validation and algorithm design activities. The hyperspectral data can be re-sampled for comparison with current and future sensor wavebands. The continuous spectral acquisition along the ship track enables spatial resampling to match satellite footprint. This study reports spectral comparisons of the radiometer data with Visible Infrared Imaging Radiometer Suite (VIIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS)-Aqua for contrasting water types in tropical waters off northern Australia based on the standard NIR atmospheric correction implemented in SeaDAS. Consistent match-ups are shown for transects of up to 50 km over a range of reflectance values. The MODIS and VIIRS satellite reflectance data consistently underestimated the in situ spectra in the blue with a bias relative to the "dynamic above water radiance and irradiance collector" (DALEC) at 443 nm ranging from 9.8ˆ10´4 to 3.1ˆ10´3 sr´1. Automated acquisition has produced good quality data under standard operating and maintenance procedures. A sensitivity analysis explored the effects of some assumptions in the data reduction methods, indicating the need for a comprehensive investigation and quantification of each source of uncertainty in the estimate of the DALEC reflectances. Deployment on a Research Vessel provides the potential for the radiometric data to be combined with other sampling and observational activities to contribute to algorithm development in the wider bio-optical research community.

Performance of Landsat-8 and Sentinel-2 surface reflectance products for river remote sensing retrievals of chlorophyll-a and turbidity

“…For water retrievals, glint corrections can cause up to 43% MAPD in R rs , significantly impacting the resulting Chl-a retrievals (Garaba et al, 2015). Little research exists on this topic for inland waters, although Overstreet and Legleiter (2017) evaluated glint corrections over shallow rivers and Brando et al (2016) evaluated glint effects in underway river samples. Harmel et al (2018) developed a glint correction that reduced bias between in situ and satellite R rs by 60%.…”

A Semi-Analytic Model for Estimating Total Suspended Sediment Concentration in Turbid Coastal Waters of Northern Western Australia Using MODIS-Aqua 250 m Data

“…The DALEC, a hyperspectral radiometer developed by "In situ Marine Optics" is used routinely for autonomous ship-based measurement of remote sensing reflectance [66]. The DALEC takes coincident measurements of downwelling irradiance (Ed), upwelling radiance (Lu) and sky radiance (Lsky) with each sensor collecting spectral information in 256 spectral bins ranging from 380 nm to 900 nm.…”

Impact of the spatial resolution of satellite remote sensing sensors in the quantification of total suspended sediment concentration: A case study in turbid waters of Northern Western Australia

“…The ship-based “Dynamic Above-water radiance (L) and irradiance (E) Collector” (DALEC) [66] was used to measure the remote sensing reflectance ( R rs , in sr -1 ) and in situ water sampling methods were used in measuring TSS concentrations. A brief description of the in situ R rs measurements using the DALEC and sampling of TSS concentration are provided below.…”