Satellite Data Analysis

Data Analysis - Satellite

The line between data analysis and remote sensing blurs for CPI activities addressing satellite measurements of emission from above 100 km. What is clearly under the heading of remote sensing is CPI's algorithm work for the DMSP SSUSI and TIMED GUVI instruments that will be used for routine data processing. Here, we cite three examples of analyses that address specific data sets but whose focus, nevertheless, is the remote sensing of either thermospheric composition or auroral energy inputs:

Polar Bear AIRS FUV disk observations of the dayglow
DE 1 FUV disk observations of the dayglow
MSX UVISI auroral limb observations

The first of these analyses is discussed in the publication by Evans et al. [J. Geophys. Res., 100, 12,227, 1995] and addresses far ultraviolet spectrometer data from the AIRS instrument onboard the Polar BEAR satellite. Simultaneous nadir observations of dayglow emission from atomic oxygen (OI 135.6 nm) and molecular nitrogen (N₂ Lyman-Birge-Hopfield) were used to derive latitudinal profiles of the abundance of atomic oxygen relative to N₂ (O/N₂). The remote sensing technique of Strickland et al. [J. Geophys. Res., 100, 12,217, 1995] based on first principles calculations using the AURIC model was used to convert the data to O/N₂. The profiles, while similar to climatological results, show structure beyond that achievable from such models.

The UVISI data analysis is discussed in the recent publication by Strickland et al. [J. Geophys. Res., 106, 65, 2001]. A specific pass of the MSX satellite through the auroral oval is addressed in which the suite of UVISI instruments made limb observations of electron and proton/hydrogen aurora. In the first image below is a snapshot from one of the instruments (visible wide imager) showing aurora on the horizon. Remote sensing techniques were applied to data seen within the region enclosed by the box. Below the first image are color displays of hydrogen Lyman a (121.6 nm) and N₂⁺ 1NG 391.4 nm seen by other instruments (spectrographs) as they viewed to the side over a period of 200 seconds (the horizontal extent of the images arises from the movement of the satellite along its orbit; a distance scale is included to reflect this motion in the form of magnetic latitude of the emitting region). The aurora seen in Lyman a and weakly at 391.4 nm is proton/ hydrogen aurora. The bright aurora at later times is electron aurora.

Image of aurora on horizon taken with
the MSX/UVISI visible wide field-of-view imager.

Proton/hydrogen aurora (centered at 235 s)
and electron aurora (centered at 310 s)
recorded by MSX/UVISI spectrographic imagers.

The analysis addresses the observed proton/hydrogen aurora and has as its objective a determination of the particle precipitation that produced the observed spatial and overall brightness characteristics seen in the data. The B3C model is used to fit calculated limb profiles to the data for selected emission features assuming uniform precipitation along the line-of-sight (see figure below). The fits, while approximate, are of sufficient quality to conclude that particle precipitation was, in fact, reasonably uniform and allowed for determination of the energy characteristics of the precipitation. A combination of proton/hydrogen and electron precipitation is required to fit the N₂⁺ 1NG 391.4 nm and N₂ 2PG 337.1 nm data. The dashed curves show the contribution from electron aurora while the solid curves show the sum of emission by electron and proton/hydrogen aurora.

Fits to MSX/UVISI limb observations for the labeled features.