Kronos: A software system for the processing and retrieval of large-scale AVHRR data sets

Raw remotely sensed satellite data have to be processed and mapped into a standard projection in order to produce a multi-temporal data set which can then be used for regional or global Earth science studies. However, traditional methods of processing remotely sensed satellite data have inherent limitations because they are based on a fixed processing chain. Different users may need the data in different forms with possibly different processing steps; hence, additional transformations may have to be applied to the processed data, resulting in potentially significant errors. In this paper, we describe a software system, Kronos, for the generation of custom-tailored products from the Advanced Very High Resolution Radiometer (AVHRR) sensor. It allows the generation of a rich set of products that can be easily specified through a simple interface by scientists wishing to carry out Earth system modeling or analysis. Kronos is based on a flexible methodology and consists of four major components: ingest and preprocessing, indexing and storage, a search and processing engine, and a Java interface. After geo-location and calibration, every pixel is indexed and stored using a combination of data structures. Following the users' queries, data are selectively retrieved and secondary processing such as atmospheric correction, compositing, and projection are performed as specified. The processing is divided into two stages, the first of which involves the geo-location and calibration of the remotely sensed data and, hence, results in no loss of information. The second stage involves the retrieval of the appropriate data subsets and the application of the secondary processing specified by the user. This scheme allows the indexing and the storage of data from different sensors without any loss of information and, therefore, allows assimilation of data from multiple sensors. User specified processing can be applied later as needed.