Field work was undertaken in the Lihou Reef National Marine Park (Coral Sea Territory, Australia, 17.583°S, 151.517°E) in December 2008. The aim of the remote sensing component of the field work was to collect in situ data for both remote sensing model parameterisation and for validation of remote sensing based results. Effort was placed on trying to characterise the (variations in) optical properties of the benthic substrates and vegetation that are part of the Lihou Reef Cay system (i.e. surrounding reefs and islands, respectively). Sample biotic and abiotic benthic types were sourced in situ in the intertidal- (exposed, above water) and the near-shore subtidal (submerged) zone. Benthic substratum reflectance spectra were measured from opportunistic samples collected in the intertidal and subtidal zone by snorkelers and divers.
Spectral data was collected with an ASD FieldSpec Pro HandHeld spectroradiometer (http://www.asdi.com) which is designed for portability and measures over the range 325 to 1075 nm with a sampling interval of 1.4nm and a Full Width at Half Maximum (FWHM) resolution of 3nm. Substratum irradiance reflectance was calculated as the ratio of the upwelling radiance (Lu) and the downwelling irradiance (Ed): Rsub = Lu/Ed
Thus the substratum reflectance is a measure of the reflection of light from the target irrespective of the illumination quantity. All measurements were collected close to the target with a 5° fore-optic fitted to the optical fibre, limiting the instrument field of view (FOV) to that of the only the target. This was done to ensure that only pure end-member spectra were collected. Ed was defined by a spectralon panel and at the same distance as the selected target. Above-water spectra were collected with the foreoptic mounted in a standard pistol-grip enabling accurate pointing of the fibre within its FOV boundaries. Reference spectra from the spectralon panel were collected at frequent intervals to compensate for the effects of variable atmospheric conditions on natural irradiance. Field spectral reflectance values were corrected for irradiance variations, assuming a linear change in irradiance over time, using these reference spectra.
Additional data collected during this field campaign included:
- Reflectance spectra of, intertidal and benthic substrates believed to be representative of the island/lagoon system using a non-submersible ASD FieldSpec handheld spectrometer as well as a submersible HydroRad spectrometer.
- Measurements were made of the optical quality of the waters within the Lihou lagoon, the individual cay lagoons of Georgina, Anne, Lorna and Turtle cays as well as the surrounding open ocean locations.
