A quick (and hopefully painless) introduction to the DMSP SSIES database
We know you wish to get to the data as quickly as you can, but please take a moment to go through this list of things you need to know before you use these data. We also urge you to read the frequently asked questions section (FAQ) for a more complete explanation about the database and the data, as well as the other pages off of the main page where we provide a more detailed background on just about everything.
The DMSP spacecraft are in polar orbits (fixed in local time) sampling the ionospheric plasma at about 840 km. F13 is in a roughly dawn-dusk orientation while F12, F14 and F15 are all in a 0930-2130 local time orientation.
The data provided here are the three components of the bulk flow of the plasma (Vx, Vy, Vz), the plasma density (Ni), the fractional composition of the plasma (percentages of H+, He+ and O+), the ion and electron temperatures (Ti and Te) as well as the time and location of the spacecraft in geographic and geomagnetic coordinates. All these data are provided at a 4 second resolution.
The data are presented in both plot form and as ascii data files. The format for the ascii data is given here.
For each 4-second group of data, there are two quality flags, one for the data derived from the RPA data (Vx, Ti, fractional composition) and the other for the data derived from the IDM (Vy and Vz). The flags are 1 (good), 2 (caution), 3 (don't use), and 4 (undetermined). In addition, the data on the plots are color-coded based on the quality flags. A complete explanation of the quality flags can be found here.
Although there are plasma data from DMSP F8 (launched 1987) onward, at this time only the data covering the time period from 1 January 2000 through 31 December 2002 are provided here. (We hope to expand this coverage soon. Meanwhile if you have a specific period outside of this time period that you wish to examine, please email us and we may be able to add that period to the database.)
During this 2000-2002 period, the Senpot device which holds the instruments at the plasma potential on F14 had failed. Thus all the data from F14 taken in daylight are suspect and flagged as poor. We are working to see if there is any way we can recover some portion of these data, but we are not optimistic.
The last point here is the most important: how reliable are these data? In an ideal world every pass in this database would have been reviewed by one of us and then either approved (making it level 2 quality data) or reprocessed until it was of satisfactory quality. However, there are a total of twelve satellite-years of data here already (and ultimately the complete dataset will have over 50 satellite-years of data) and there are only two of us (Drs. Hairston and Coley) working on this project part-time. There is simply no way we can do that given the limits on our time. So we have done the next best thing: we have developed an automatic routine which evaluates the quality of each 4 second datum from the RPA and IDM as described above. Although this routine is automatic, we have designed it to err on the side of caution, thus if there is the slightest question about a datum it is flagged as caution (flag=2), poor (flag=3), or undetermined (flag=4). Essentially all of the data marked as good (flag=1) are most certainly good and can be used with a high degree of confidence. As you will see after examining several of these orbital plots, once something happens to the data, such as the light ion percentage starts to increase or the Senpot device fails in sunlight (as happened on F14 in the 2000-2002 period), the quality of the data goes down quickly and significantly, and there is simply not much we can do to salvage these data by reprocessing. Thus, while we will be refining this quality algorithm over the next several years, it is doubtful that more than a few percent of the data currently labeled as "caution / poor / undetermined" will ever be reclassified as good.
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