Since 1981 the NOAA Polar Orbiting Environmental Satellites (POES) have carried a series of 11 AVHRR instruments providing daily global observations in four or more spectral bands at 1.1km resolution. Data from these spacecraft has been acquired at several reception stations in the Australasian region since the mid-1980s. The EOC has collated these data, and by supplementing them with 5km AVHRR/GAC data recorded by NOAA, has assembled the most comprehensive time series of observations possible. The data are fully catalogued and indexed and stored uniformly in the Australian Satellite Data Archive format on multiple sets of DLT tapes.
EOC staff and collaborators are actively developing implementations of the current best-practice processing algorithms for inclusion in the CSIRO AVHRR Processing Systems (CAPS) software. The particular areas being addressed are base data quality, calibration, geolocation, cloud detection, and correction for atmospheric and view/illumination geometry effects. The goal is to be able to perform the base processing of the AVHRR image data to a high standard throughout the time series.
Overall longitudinal internal consistency is a particular focus of this work. Many factors influence satellite-based observations, including sensitivity and spectral variations between instruments, long-term variation of sensitivity over the lifetime of each individual instrument, and changes in the illumination and viewing geometry resulting from evolution of the orientation satellite orbits with respect to the sun. It is essential that the contributions of all these effects be minimised and quantified so that maximum value can be made of the capability of a long time series to detect subtle trends.
To improve access to the data set and products, the EOC has engaged in a collaborative project (Web-CATS) with CSIRO Land and Water, to develop a Web-based delivery system. The entire data set resides on the nodes of a PC-based cluster of computers which perform the base processing and product generation in parallel in response to user request via the web site. The product is then delivered over the Internet. To ensure applicability and relevance, this system is being developed in close association with a number of client projects (encompassing regional hydrology, model-data fusion and Earth System Science).
The POES/AVHRR program will continue until around 2010. Before then, beginning in 2006, the first spacecraft of the replacement National Polar Operational Satellite System (NPOESS) will be launched. The higher data rates and more advanced sensors carried on these satellites will bring new challenges in terms of efficient data management and new opportunities for data utilisation. The EOC is seeking to develop, ahead of time, the expertise and techniques that will be needed to manage and exploit these rich new data sets. Of key importance will be the methods used to enable a seamless transition for applications from the AVHRR-derived datastream to that from NPOESS.