# Tools and Models:Emmert sat drag neutral mass density

Neutral density data from satellite drag studies using ~5000 objects were performed by John Emmert (john.emmert@nrl.navy.mil, 202-767-0467, U. S. Naval Research Laboratory, Washington, DC, USA) and described in

**Emmert, J. T. (2009), A long-term data set of globally averaged thermospheric
total mass density, J. Geophys. Res., 114, doi: 10.1029/2009JA014102.
(.pdf of paper).**

Abstract:

We present a long-term data set, available on the CEDAR Data System, of globally averaged thermospheric total mass density derived from the orbits of ~5000 objects. The data cover the period 1967-2007 at heights from 200 to 600 km. The data have a temporal resolution of 3-6 days, a typical short-term precision of 2%, and a long-term accuracy of 5-10%. We describe in detail the procedure used to generate the data set, provide an example of its scientific use, and discuss its limitations.

The data are actually parameterized height profiles that cover the 200-600 km interval and were processed as:

- A time series of density ratios is inferred from each of the 5000 objects. The ratio is representative of conditions near the perigee of each orbit (actually a little above perigee for elliptical orbits).
- The ratios from all objects are combined into a parameterized average as a function of height and time. Since the collection of objects covers the entire globe, this is a 'global average ratio'.
- The global average MSIS density (NRLMSISE-00) is computed, and the ratio is applied to obtain the absolute global average density at each desired height.

The reference for the NRLMSISE-00 model is:

**Picone, J. M., Hedin, A. E., Drob, D. P., Aikin, A. C., (2002), NRLMSISE-00
empirical model of the atmosphere: Statistical comparisons and scientific issues,
J. Geophys. Res., 107(A12), 1468, doi: 10.1029/2002JA009430.**

Values of the neutral mass density from the MSIS (NRLMSISE-00) model and satellite drag objects are in log10 units of Kg/m3, where ratio=MSIS/drag (not the ratio of the log10 values, but the values themselves).

**Acknowledgements:** This study made use of the CEDAR Database at the National
Center for Atmospheric Research which is supported by the National Science Foundation.

**Rules of the Road **require contact with the data provider (john.emmert@nrl.navy.mil)
about possible co-authorship and use of the data, as well as citing the Emmert (2009)
paper.

The lists include values for the following parameters from day 1 in 1967 to day 279 in 2007. More recent lists are available from john.emmert@nrl.navy.mil

year day ut ratio uncert log10(msis) log10(drag) uncert

- Daily 250 km neutral mass density in log10(kg/m3) from MSIS00 and satellite drag objects from 67001 to 07279 (~1.1MB)
- Daily 400 km neutral mass density in log10(kg/m3) from MSIS00 and satellite drag objects from 67001 to 07279 (~1.1MB)
- Daily 550 km neutral mass density in log10(kg/m3) from MSIS00 and satellite drag objects from 67001 to 07279 (~1.1MB)