Baseline plots for 22 sensors | Description of 22 sensors
The second generation Space Environment Monitor (SEM-2) onboard the polar-orbiting NOAA POES satellites makes observations continuously and, over the course of one year, gathers data from about 5200 satellite orbits of the satellite around the Earth. The amount of data is sufficient to obtain statistically significant one-year median particle intensities at all geographic locations on the globe, at geographic latitudes between about 82° in the north and the south.
To find the one-year median values, the globe is sectored into bins that are 5° in longitude and 2° in latitude. The responses of all 22 energetic particle channels during the course of one year are accumulated whenever the sub-satellite location is within each of these bins. Data taken when the satellite is northbound through a bin are kept separate from data taken during southbound transits. This is done because when the NOAA POES satellite samples a given location on the globe at a local time that depends on whether the satellite is northbound or southbound. Combining observations from the same location but at different local times would mask any dependence of particle intensities on local time. In addition, the angle between the geomagnetic field and the view direction of the 90° particle telescopes also depends on whether the satellite is northbound or southbound, and so combining observations would obscure any dependence of particle intensity on the detector's angle with respect to the geomagnetic field.
Over the course of a year, the satellite passes through each 2° by 5° latitude-longitude bin on the globe at least 150 times in each direction. For each of the 22 detector channels, median values of the 150 (or more) samples taken during the year for each bin form a baseline data set to which observations made at a specific time and place can be compared. The one-year baseline data set is updated approximately each month, using the most recent observations.