Survey number: AK21 and AK22 (Pat Hill numbers)
Name: Prudhoe Bay Region (AK21) and Arctic Natl Wildlife Refuge (AK22)
Date flown: July 11-21, 1981
Company: USGS (Beechcraft E50, twin-engine aircraft)
Flight specs: 1-3 mi spacing, E-W in ANWR, N-S in Prudhoe Bay Region,
              300 ft above ground

Digital data source: NGDC file 0260-926

Publication reference: Donovan, T.J., Hendricks, J.D., Roberts, A.A., and
Eliason, P.T., 1984, Low-altitude aeromagnetic reconnaissance for petroleum 
in the Arctic National Wildlife Refuge, Alaska: Geophysics, v. 49, n. 8, 
p. 1338-1353.

Ascii data fields:

1. Flightline number (i4) [a4]
2. Longitude [f10.4]
3. Latitude [f9.4]
4. Tail mag (total field, nT) [f9.2]
5. Left wing mag (total field, nT) [f9.2]
6. Right wing mag (total field, nT) [f9.2]
7. Radar altimeter (ft) [f5.0]
8. Julian date (day of year) [f5.0]
9. Leveled mag (arbitrary datum, nT) [f8.2]

Fortran format:
(a4,f10.4,f9.4,3f9.2,f5.0,f5.0,f8.2)

Data fields 1-8 are from NGDC data file.

Data field 9 (Leveled mag) is based on line-leveling of field 4 (tail mag)
after application of DGRF for the time of the survey.  The line-leveling
was done by comparison with regional data from two proprietary surveys
for this area.  The best-fitting DC offset was applied to each survey
line to match it to the average levels of the proprietary surveys.
This procedure leaves some obvious flightline noise that will require
filtering for production of a smooth grid.  The large-amplitude basement
anomaly centered at about 70 N and 145 W should be smooth.  It can be
used as a guideline for filtering.

[Line-leveling done by Rick Saltus, USGS, 16 October 1996]