Operations Updates
ARM Climate Research Facility Operations Update - August 15, 2004
This bimonthly report provides a brief summary of significant accomplishments and activities in the operations area of the ARM Climate Research Facility (ACRF).
SuomiNet-type Instruments Tested and Ready for Tropics
The SuomiNet software integrates a network of global positioning systems to distribute spatially and temporally dense atmospheric data in real-time from broad and diverse regions.
ARM Program scientists are concentrating on developing techniques for obtaining the best possible water vapor measurements under a wide range of conditions (clear/cloudy, day/night, etc.). In 2001, 15 SuomiNet systems were installed at selected facilities at the ACRF Southern Great Plains (SGP) site to obtain these measurements (see photo at right). SuomiNet is an international network of global positioning system (GPS) receivers and meteorological instrument packages, configured and managed to generate near real-time estimates of precipitable water vapor in the atmosphere, total electron content in the ionosphere, and other meteorological and geodetic information. To acquire total column water vapor measurements at its Tropical Western Pacific (TWP) sites, the ACRF is deploying a similar system developed by COSMIC, including GPS and meteorological packages (from Paroscientific).
The COSMIC system is based on the Trimble netRS receiver, which incorporates a linux system that permits the receiver to be connected directly to the network, eliminating the need for a separate dedicated computer for communication and data transfer.
To ensure compatibility with the existing SuomiNet data processing systems, ACRF operations staff began working with COSMIC representatives in July to configure and test the systems at SGP prior to deployment to the tropics. Siting requirements, such as a clear view of the sky down to an elevation angle of 5 degrees, the need to be away from metal structures, etc., were considered in the testing. Testing was successfully completed, and installation at TWP will occur once the final setup designs and necessary operations and maintenance documents are delivered to site operations staff.
Approximately one megabyte of data for each SuomiNet site will be delivered with the new system each day. These additional data will help ARM researchers quantify improvements to clear sky radiative transfer, which are currently limited by the uncertainty in atmospheric water vapor distribution profiles.
Fancy Footwork Accomplishes Scheduling Feat for ER-AERI
Thanks to quick actions on the part of numerous ACRF operations staff, an Extended Range Atmospheric Emitted Radiance Interferometer (ER-AERI) is on its way to Oliktok Point, Alaska. As part of an ongoing instrument comparison, two ER-AERIs (one a permanent ARM instrument, the other a "visitor") have been operating side by side since January 2004 at the ACRF North Slope of Alaska's Barrow site. The visiting ER-AERI (from the University of Wisconsin) and the instrument shelter developed for it at Barrow were slated for barge transport to Oliktok in late August to support ARM's Mixed Phase Arctic Cloud Experiment (M-PACE). In late July, the team was surprised by a notice from the barge company that their departure date from Barrow had moved up about three weeks, to the August 6 timeframe. Following a flurry of phone calls and some scrambling of schedules, the AERI instrument mentor essentially dropped everything and managed to arrange a flight up to Barrow to disassemble and pack the ER-AERI components in time for the barge trip. The alternative of delaying shipping and transporting the equipment and shelter by plane to Oliktok would have cost around $30K (vs. $3K by barge), potentially precluding the use of the instrument during the experiment.
As part of M-PACE, the ER-AERI will join a suite of remote sensing instruments, aircraft, and balloons (tethersonde and radiosondes) to collect in situ observations of mixed-phase stratus cloud properties. A "typical" AERI measures the spectral radiance of the sky directly above the instrument in the range of 20-3 microns; the ER-AERI is suited for the reduced water vapor concentration in the Arctic atmosphere and viewing into the so-called "dirty window" from 18 to 25 microns. The AERI shelter, which consists of a partitioned insulated shipping container, will also house the radiosonde system and provide onsite shelter for the Oliktok operations crew during the experiment.
New Narrow Field of View Radiometer Widens Range of Radiance Data
Development of the new 2-channel NFOV (right) benefited greatly from a comparison with the original 1-channel version (left).
Development of a new, two-channel narrow field of view (NFOV) radiometer for the ACRF Southern Great Plains site is nearly complete. The two-channel NFOV replaces a similar single-channel instrument that was destroyed by lightning in June 2002, and adds a 673 nm (red) measurement to the measurement at 870 nm (near infrared). Repairs to the original NFOV were completed and calibrated first, so that it could be used to check the calibration of the 2-channel version. This comparison proved to be a very valuable step, as it revealed a subtle electronics problem in the new version that caused a drift in the readings. With the problem solved, completion of the new instrument is imminent, and deployment at SGP is anticipated in September.
Development of the two channel unit required construction of new instrument housing and incorporation of a new data logger. The new NFOV radiometer collects data using a CR10X measurement and control system (from Campbell Scientific). Instrument output consists of a time series of 1-second observations of zenith spectral radiance. These radiance data can be used to characterize the optical properties of clouds. The additional 673 nm radiance measurement is an important element in developing cloud optical depth algorithms and retrieval methods, particularly for broken cloud fields.
