Since October 1998, the MkIV instrument has been making ground-based observations from Mt. Barcroft, at 3801 m (12450 feet) altitude in the White Mountains of California. This site, 400 km North of Los Angles and 350 km East of San Francisco, is away from the main population centers and is therefore relatively unpolluted. Its high altitude makes it easier to measure the stratospheric trace gases of interest by reducing interfering absorption by tropospheric major gases such as H2O, CO2: (1) the overburden of atmospheric water vapor is an order of magnitude less than above an equivalent sea-level site, (2) the low surface pressure (~630 mbar) reduces linewidths, (3) the cold temperatures greatly reduce absorption by temperature-sensitive lines.
The MkIV instrument is housed inside its trailer, outside the Mt. Barcroft Research Station (run by the University of California, San Diego). The MkIV is controlled remotely from JPL over a cellular phone or the internet. The MkIV views the rising Sun through a 6" diameter ZnSe window mounted in the rear door of the trailer. In this configuration, ~2 hours of data can be acquired every clear morning. The MkIV instrument is powered by 28 lead-acid batteries (each 115AH) recharged by 18 solar panels (each 55W). This provides reliable power for running the MkIV instrument and GSE, and for maintaining the MkIV instrument at its 25C operating temperature throughout the winter. Since October 1998, more than 250 days of observations have been obtained by the MkIV instrument from Mt. Barcroft.
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