PROCESSING.TXT The SNOE data files have passed through five steps of processing in order to reach their final state. Those steps are described in this file. The initial spacecraft data are processed into the Level One (L1) data files. Further processing results in the Level Five (L5) product. ______________________________________________________________________________ PRODUCT: Ultraviolet Spectrometer Count Rates Level One Data GENERAL DESCRIPTION: The Level One Data files are created by processing the spacecraft data into an altitude registered science database. DETAILED DESCRIPTION: The individual scans from the UVS instrument are retrieved from the S/C Database. Each scan has an associated latitude, longitude, magnetic latitude and longitude, and UTC timestamp. Each scan consists of 100 samples (counts/integration period [http://lasp.colorado.edu/snoe/lib/instruments.html#UVS]) from approximately 0 to 200 km. A scan is triggered by the Horizon Crossing Indicator (HCI) on board the spacecraft. See http://lasp.colorado.edu/snoe/lib/ADCS.html for more information on the HCI. The Command and Data Handling computer (C&DH) waits for the S/C to rotate to the correct position, and then begins the sampling of the scan. Due to variations in the HCI sensor and spin rate, the exact altitude of the start and stop locations of each scan is uncertain. Each scan needs to be calibrated against an altitude scale. This is done by comparing the scan against a model that covers a part of the atmosphere sampled in the scan. This atmospheric region has a well defined signature and is recognizable in both the scan and the model. The recognized signature is the Rayleigh scattering peak as measured with the UVS. Linear interpolation is used to shift each scan from its measured values onto a known altitude scale based upon the model. Scans containing anomalous data (PMCs, the Moon, planets, stars, or unrecognizable signatures) are discarded from the data set when identified. Each altitude-registered scan is then recorded into the L1 Science Database, with its associated geographic latitude and longitude, magnetic latitude and longitude [http://nssdc.gsfc.nasa.gov/space/cgm/cgm.html], solar zenith angle, UTC time, and other science, engineering, and processing information. The 15 orbits of each day are also identified. A SNOE day begins at the first south-bound equator crossing after 00:00 UTC. Each orbit starts at this point, and continues to the the same latitude (minus one scan) on the next orbit. ______________________________________________________________________________ PRODUCT: Nitric Oxide Column Density Level Two Data GENERAL DESCRIPTION: The Level Two Data files are latitude and orbit binned files. They maintain altitude resolution and each latitude bin has the average longitude of the binned scans recorded. DETAILED DESCRIPTION: The individual SNOE spins, each with an associated latitude, longitude, magnetic latitude, and magnetic longitude coordinate are summed in their respective coordinate systems, into 5 degree bins. The model is then subtracted so that only the nitric oxide radiance remains, and the data is normalized to the model at an altitude of 73.3 km. The radiance is converted to NO column density by using the emission rate factor (g-factor). ______________________________________________________________________________ PRODUCT: Nitric Oxide Volume Density (molecules/cm^3) Level Three Data GENERAL DESCRIPTION: The Level Three Data files have the same layout as the Level Two files. However, the data has been translated from the spacecraft look angle to a volume density at the recorded latitude and longitude. DETAILED DESCRIPTION: The science data is translated from the SNOE look angle (through the atmosphere at the limb of Earth) into a volume density. Any data outages of size one (i.e. all adjacent neighbors contain valid data) in the dataset are filled in using linear interpolation in the altitude direction. ______________________________________________________________________________ PRODUCT: Daily Averages of Nitric Oxide Density (molecules/cm^3) Level Four Data GENERAL DESCRIPTION: The Level Four Data files contain latitude and altitude resolution. DETAILED DESCRIPTION: All orbits for a given day of Level Three Data that contain valid data are averaged together for each day of Level Four Data. Any data outages of size one (i.e. all adjacent neighbors contain valid data) in the dataset are filled in using linear interpolation in the latitude direction. ______________________________________________________________________________ PRODUCT: Nitric Oxide 3D Volume (molecules/cm^3) Level Five Data GENERAL DESCRIPTION: The Level Five Data Files contain latitude, longitude, and altitude resolution. DETAILED DESCRIPTION: Data from the Level Three files contains the average longitude of each 5 degree latitude bin. For each altitude between 96.6 iand 150.0 km a slice of data is taken from all latitudes and orbits. The data is translated from its recorded longitude grid to a predetermined grid. The longitude grid the data is interpolated onto has 15 bins, from -168 to 168 degrees, in steps of 24 degrees. The bins are centered at -168, -156, ...,-12, 12, 36, ..., 156, 168. The data maintains its 5 degree latitude bins. Any data outages of size one (i.e. all adjacent neighbors contain valid data) in the dataset are filled in using linear interpolation in the longitude direction. The reslult is a 3D volumetric dataset of NO volume densities.