Processing Overview ******************* This section describes the basic procedure that Geona Hyperspectral follows when applying to the raw sensor data up to he geocrectified map data. Before describing the processing procedure it is prudent to discuss some of the file formats used. BIL / BSQ files --------------- The raw sensor data is provided as an ENVI BIL format. This is a flat binary file with an accompanying header file (.hdr) that is a plain text file that describes the shape and type of the binary file and also contains other metadata relating to the binary data (for details see https://www.nv5geospatialsoftware.com/docs/ENVIImageFiles.html). The data used in Geona are either BIL (band interleaved by line) or BSQ (band sequential) and can easily be imported into GIS systems, Matlab, Python or any tool that uses the GDAL library. The header (hdr) files ^^^^^^^^^^^^^^^^^^^^^^ The header files contain the information to be able to decode the binary data but, importantly, Geona also writes metadata in to these that are used in the processing of the data or important for post-processing tasks. Information on non-Geona specific header items can be found at https://www.nv5geospatialsoftware.com/docs/enviheaderfiles.html. Radiometric Calibration ----------------------- The first step in processing the data is to convert from the raw digital numbers (DN) into a real-word meaningful value. To do this, the software requires a calibration gains file specific to the sensor detector, and applies these gains together with other sensor specific methods resulting in a radiometrically calibrated data file (sometimes referred to as a level1 file). In addition to this file, Geona will also generate a mask file. This file is an 8-bit binary flag file describing the status for each image pixel. The mask files been produced at the radiometric calibration stage and the masks are applied in the masking stage to ensure that poor quality data are not being used. However, this is regarded as an optional step and can be missed out. It is possible to mask pixels based on all the failure types or to mask using a subset of them. The masked data are set to 0 in the masked file. The :ref:`Only use specific flags ` option is available for this purpose. Georeferencing and Reprojection ------------------------------- The georeferencing procedure is concerned with assigning each pixel of the calibrated data a latitude and longitude. To do this there are two stages that must be completed: navigation synchronisation and geocorrection. Navigation synchronisation is the procedure of assiging a per-scan-line position and attitude of the sensor platform to the calibrated data. After this it is possible to assign a latitude and longitude to each pixel using either an ellipsoid model or a digital elevation model. The resulting file is an IGM file, a three band BIL file where each pixel has a latitude, longitude and elevation. It is possible to reproject the IGM data into another coordinate system if required. Resampling ---------- Resampling is the stage that generates a map product in the specified coordinate system.