GBI 4 Channel Photometers for TIMED

Jim Hecht (james.hecht@aero.org) of Aerospace Corporation is responsible for the analysis of 4 channel filter photometers located at:

  1. Poker Flat, Alaska (65.12N, 212.57E, 65.4mlat) and Aerospace plots up to last night
  2. Fort Yukon, Alaska (66.6N, 214.7E, 67.6mlat) and Aerospace plots up to last night
  3. Sondre Stromfjord, Greenland (67.0N, 309.0E, 73.0mlat)
The first two instruments are Aerospace instruments, while that in Sondre Stromfjord is run by Gary Swenson (swenson1@uiuc.edu), although the brightness data are analyzed by Jim Hecht.

The 4 channel filter photometers were developed to estimate the energy flux of auroral electrons, their average energy Eo (usually from 0.1 to 30 keV using a modified Gaussian or Maxwellian shape), and a scale factor fo for the atomic oxygen densities [O] from an MSIS model atmosphere. The [O] densities using the scaling factor fo can be compared to GUVI/TIMED estimates. The technique is only valid for clear night conditions where the solar zenith angle is greater than 102 deg, and there is sufficient 427.8 nm emission. The photometer looks up the magnetic field line with a field of view (fov) of about 1 deg. The data rate can be programmed, but typically each channel is integrated for 1 sec, where the whole cycle including filter moves takes about 8 sec.

The 4 channels correspond to:

  1. N2+ (427.8 nm, blue) first negative group (1NG) 0,1 molecular band
  2. OI (630.0 nm, red) forbidden
  3. OI (844.6 nm, eight) permitted
  4. N2 (871.0 nm or 871.4 nm) first positive group (1PG) 2,1 molecular band
The brightness is converted from counts/sec to R, a standard background is removed, and the brightness is then corrected for atmospheric scattering. The corrected 427.8 nm brightness is directly related to the incoming auroral electron energy flux, but the mean electron energy Eo and the [O] scaling factor fo are complex functions of the model conditions and the ratios of the calculated red/blue (6300/4278) and eight/blue (8446/4278) emissions.

More complete information is given in the Poker Flat website with one example from April 15, 2001 completely accessible, and Oct-Dec 2001 plots for good nights only. The Aerospace web page is located at http://gedds.pfrr.alaska.edu/aerospace.

Site Lat Lon Type Kinst Contact
Poker Flat, AK, USA 65.12 -147.43 4CFP 4470 J. Hecht
Fort Yukon, AK, USA 66.6 -145.3 4CFP 4473 J. Hecht
Sondrestrom, Greenland 67.0 -51.0 4CFP 4476 J. Hecht

--Revised 05 Oct 2004 by emery@ucar.edu