DOI: 10.1594/pangaea.873219
title: Estuarine macrophytes and saltmarsh vegetation reflectance spectra collected at Wallis Lake (NSW, Australia)

description: Wallis Lake is a shallow estuarine lake system consisting of lakes and rivers with interconnecting channels. The lake is a significant environmental resource and is also used for recreational activities and aquaculture.In collaboration with participants from NSW DPI, CSIRO undertook a fieldwork campaign at Wallis Lake 12-16 May 2008 to fill in known gaps in saltmarsh, mangrove, seagrass and macro-algae spectra as well as abiotic backgrounds such as sand and mud. Benthic material were collected with an Eckman grab, where the structure and shape of the sample was retained. Samples were placed on a black neoprene mat and spectra were collected using a RAMSES spectroradiometer. The RAMSES spectroradiaometer system deployed at Wallis Lake consisted of two cosine collector sensors measuring downwelling irradiance (Ed) and one radiance collector measuring upwelling radiance (Lu). In situ spectral reflectance of intertidal and supratidal vegetation were collected with an ASD-FR FieldSpec Pro spectroradiometer system which measures over a range of 325 to 2500 nm. To fill in data gaps, additional supratidal substratum spectra were collected in September 2008 with an ASD FieldSpec Pro HandHeld spectroradiometer (www.asdi.com). Substratum irradiance reflectance was calculated as the ratio of the upwelling radiance (Lu) and the downwelling irradiance (Ed): Rsub = Lu/EdThus 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 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. Data collected during this field campaign included: - Inherent optical properties (IOP) and apparent optical properties (AOP) measurements of water quality in representative waters of Wallis Lake and rivers _ Reflectance measurements of seagrasses, algae and mud/sand collected with a RAMSES - field spectrometer - GPS depth transect across Posidonia beds on the eastern boundary of Wallis Island. - A pseudo invariant feature (PIF) measurement on the Wallis Island airstrip was collected to assist in the atmospheric correction of the 2003 Quickbird imagery which had exhibited significant calibration issues and could not be successfully corrected for atmospheric effects by standard methodologies undertaken by CSIRO. The reflectance values collected at the airstrip was assumed to represent reflectance at the time when the satellite image was collected. - Terrestrial reflectance spectra of saltmarsh and mangrove species as well as other key species present were collected with an ASD field spectrometer for inclusion in the spectral library as well as for validation purposes.