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When studying the Earth's surface from space it is important that the component of the signal measured by the satellite-based sensor due to the atmosphere is accurately estimated and removed. Such atmospheric correction requires good knowledge of atmospheric parameters including precipitable water (PW), ozone concentration and aerosol optical depth. To make full use of the capabilities of satellite sensors such as the Moderate Resolution Imaging Spectroradiometer (MODIS) these parameters should be accurately estimated in Near-Real Time (NRT) with complete global coverage approximately every two days. NRT retrieval of the required ancillary information facilitates the atmospheric correction of such direct broadcast data from the MODIS instrument in the operational environment. In this paper three Near Infrared (NIR) algorithms for PW retrieval from MODIS are compared to determine which is most suitable for use in an operational MODIS-based process for the atmospheric correction of spectral reflectance data. Two of the algorithms estimate PW in NRT and gave RMS errors of approximately 0.48 g cm 22 (23%) and 0.59 g cm 22 (28%), respectively, when compared against radiosonde data and modelled PW fields over Western Australia. The third algorithm was the NIR PW product from MODIS (MOD05) archived by the Distributive Active Archive Centre (DAAC). For the same locations the MOD05 NIR PW dataset gave an RMS error of approximately 0.95 g cm 22 (44%). In each of the cases the best results were obtained after optimal cloudmasking of the NIR data. In this paper, the accuracy and suitability of the three algorithms for use in the operational atmospheric correction of MODIS data are evaluated and the importance of an accurate cloudmask for atmospheric correction in NRT is discussed.

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The optical properties of sea water, including ocean color (chlorophyll concentration), diffuse attenuation coefficient, and surface/subsurface reflectance, may be readily estimated from space-borne sensors (eg. SeaWiFS, MODIS) in the open ocean (Case 1 waters). However, in near-shore and shallow waters (Case 2), the presence of other organic materials and suspended sediment, as well as bottom reflection, may affect the spectrum of water-leaving radiance making estimation of optical properties based upon multispectral measurements more complex. In this work, we investigate the impact of these additional components on the water-leaving radiance and associated optical properties of the ocean using; i) in situ measurements of the optical properties of the water column, and; ii) modelling of the radiance field within marine environments typical of Case 2 waters off the coast of Western Australia. This paper presents results from the investigation so far including data acquired during a number of oceanographic cruises in Western Australian waters. We conclude by suggesting the way forward for the remote sensing of ocean color in near-shore and shallow waters in Western Australia.