GACP Datasets

Halthore Dataset

Subject: REVISION: Release Notice - Cloud Screened Sunphotometer data product
Date: May 25, 1999
To : ARM Science Team
From: ARM Experiment Center

RE : Revised Release Notice for CSPHOT Cloud Screened Data

Cloud-screened Cimel sunphotometer (CSPHOT) data from the SGP site are now available for distribution from the ARM Experiment Center. The data are named according to sgpcsphotaotpwfiltX1.00.YYYYMMDD.hhmmss.raw.asc

Data include aerosol optical thickness (AOT) as a function of 7 wavelengths (340, 380, 440, 500, 670, 870, and 1020 nm) and precipitable water in centimeters derived from measurements in the 940 nm band. The data are preliminary and have been filtered for the presence of clouds according to a set of criteria described in Smirnov et al. (Cloud screening and quality control algorithms for the AERONET data base, submitted to Remote Sensing of Environment, Sep 1998). Briefly, these criteria include restricting the variability in a triplet measurement of AOT taken 30 s apart to less than 0.02, restricting the Angstrom exponent (computed between 440 and 870 nm) to between 0.0 and 3.0 and restricting the variability in AOT at 550 nm during day to less than 3 standard deviations of the daily mean. In addition, data sets with AOT values below 0.005 are removed. There is a possibility that these criteria may be more restrictive than necessary for a given application. So caution should be exercised in use of this data. For best results consult unscreened raw data as well. Note that the values may change when post-field calibration is applied.

Data cover periods 4/6/94 - 5/2/94, 4/10/96 - 5/2/96, 9/6/96 - 9/30/96, 9/13/97 - 10/21/97, 3/12/98 - 3/13/98 and 4/10/98 - 9/30/98. Since March 1998, Cimel sunphotometer has been permanently installed at the SGP CART site. It will be shipped frequently to Goddard Space Flight Center for annual calibration by intercomparison with an instrument that has been calibrated at Mauna Loa.

On some days in the 1998 data significant gaps near solar noon are the result of faulty satellite transmitter operation.

Details of the instrument, its operation and data units can be obtained from the ARM Instrument page at

At present only data from the SGP CART site is included in this release. Efforts are underway to salvage useable data from the Barrow site in Alaska. Because of continuous bad weather and instrumental problems, the number of days with useable data is limited.

If you would like to receive this data, please contact the Experiment Center staff (, 888-ARM-DATA/888-276-3282) to open a new, or modify an existing, Experiment Operations Plan.

Data can also be obtained from the AERONET web site at:

Questions regarding the data may be directed to:

R. N. Halthore