Field Sunphotometer
OTTER Data Description
Field sunphotometer data were acquired during the OTTER Multi-sensor
Aircraft Campaigns (MAC) in 1990 and 1991. Sunphotometer data were
acquired concurrently with ER-2 (TMS and AVIRIS) and C-130 (ASAS and
NS001) overpasses, when possible. In addition, some of the sunphotometer
measurements were acquired simultaneously with ultra-light flights
(Barnes MMR and Spectron 590 and 393). Two sunphotometers were used
during the OTTER MAC; both were manufactured by Dr. John Reagan at the
University of Arizona. Measurements made by the two sunphotomers are
nearly identical, therefore, data from instruments 1 and 2 can be used
interchangeably.
The sunphotometers are ten channel filter wheel instruments which are
operated manually. They measure direct incoming solar radiation with
10 nm filter bandpasses centered at 370, 400 440, 520, 610, 670, 780,
870, 940 and 1020 nm. The 940 nm channel is not calibrated; this
channel should not be used until further notice.
The instruments were calibrated at Mt. Shasta on June 21 and June 22
using the Langley plot technique. Details of the calibration procedure
and processing of the sunphotometer data are found in Spanner et al.,
1990, Journal of Spacecraft and Rockets, 27(4):373-379. Sunphotometer
data were acquired at each OTTER site during the aircraft overflight
periods in February, March, June, August and October of 1990 and in
May and June of 1991. Sunphotometer measurements were made approximately
every 5 minutes for a minimum of 20 minutes at each OTTER site. 1-2
minutes were required to acquire data in all ten channels. In this
manner, all six OTTER sites were covered by two sunphotometers once or
twice each day.
The sunphotometer data provided to PLDS were processed using A10
software developed by John Reagan's group at the University of Arizona.
The format of the processed data was modified to conform to the Pilot
Land Data System (PLDS). The following fields are associated with each
data record which corresponds to a 1-2 minute measurement period for all
ten channels of the sunphotometers.
Date: Date when sunphotometer data were acquired
(ie. 8/13/90).
Site: Site where sunphotometer data were acquired
using the site numbers plus the PLDS site
description code, (ie 1-CH, 2-WW, 3-SC, 4-SP,
5-ME, 6-JU).
Instrument: Instrument that made measurement (ie. Reagan1
or Reagan2).
Time: Pacific Standard Time for data acquired in
February and March. Pacific Daylight Time for
data acquired in June, August and October.
Local time is given in the PLDS database as
LOCAL DATE. Greenwich Mean Time (GMT) is
also given.
Solar Angle: Solar elevation during acquisition period.
Airmass: Atmospheric airmass.
Rayleigh Optical Depths: For wavelengths at 370, 400, 440, 520, 610,
670,780, 870, 940 and 1030 nm. Calculated
from atmospheric pressure and solar elevation.
Net Optical Depths: For wavelengths at 370, 400, 440, 520, 610,
670, 780, 870, 940 and 1030 nm. Net Optical
Depth is equivalent to the aerosol optical
depth. The Net Optical Depth is calculated
from the total optical depth minus the Rayleigh
optical depth, ozone optical depth and nitrogen
dioxide optical depth. Ozone optical depth is
calculated from the climatological tables of
(Van Heuklon, 1979, Solar Energy, 22:63-68).
Nitrogen Dioxide optical depths calculated from
(Noxon, 1979, Journal of Geophysical Research,
84:5067-5076).
Note: Data collections listed in PLDS for the Metolius site were
actually gathered at the Sisters airport. The latitude and longitude
given is for the airport.
Dates of Collection (GMT):
2-22-90
3-21-90
6-18-90
6-19-90
6-20-90
6-21-90
6-25-90
6-26-90
8-13-90
8-14-90
8-15-90
10-8-90
5-22-91
6-9-91
6-10-91
Any questions regarding these data should be addressed to Michael
Spanner at 415-604-3620 or MASPANNER@ames.arc.nasa.gov.