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Fred V. Brock, George H. Saum, and Steven R. Semmer

Abstract

The Portable Automated Mesonet II (PAM II) system was developed by NCAR to provide surface mesoscale data for the research needs of the atmospheric science community. The PAM system has 60 remote stations with planned growth to 300. In such a distributed system, data communication is a vital subsystem and, since it dictates some key system constraints, deserves special attention. The NOAA/NESDIS satellite, GOES, is used to link the remote stations to the base stations. This provides very wide areas coverage but limits the data rate.

Special attention was given to the design of the sensor subsystems to minimize the possibility for human error and to maintain the calibration in field conditions while using interchangeable modules. This was achieved by using a dedicated microprocessor in the psychrometer and the barometer. The microprocessor in the sensor modules controls the sensors, applies the individual calibration coefficients, and transmits the sensor data to the master data acquisition module.

The master base station collects the data, archives them and generates graphic displays of real-time or archived data for system control and scientific analysis. The field base stations provide real-time data for the user in the field environment.

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Scott J. Richardson, Fred V. Brock, Steven R. Semmer, and Cathy Jirak

Abstract

Multiplate radiation shield errors are examined using the following techniques: 1) ray tracing analysis, 2) wind tunnel experiments, 3) numerical flow simulations, and 4) field testing. The authors’ objectives are to develop guidelines for radiation shield and temperature sensor design, to build an improved shield, and to determine factors that influence radiational heating errors. Guidelines for reducing radiational heating errors are given that are based on knowledge of the temperature sensor to be used, with the shield chosen to match the sensor design.

A new class of shield called a part-time aspirated multiplate radiation shield is introduced. This type of shield consists of a multiplate design usually operated in a passive manner but equipped with fan-forced aspiration capability to be used when necessary (e.g., low wind speed). A prototype shield reduced radiational heating errors from 2° to 1.2°C. In addition, nighttime low wind speed errors were reduced from 1.6° to 0.3°C. Existing passive shields may be modified to incorporate part-time aspiration, thus making them cost effective.

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Sean P. Burns, Anthony C. Delany, Jielun Sun, Britton B. Stephens, Steven P. Oncley, Gordon D. Maclean, Steven R. Semmer, Joel Schröter, and Johannes Ruppert

Abstract

The construction and deployment of a portable trace-gas measurement system (TGaMS) is described. The air-collection system (dubbed HYDRA) collects air samples from 18 different locations and was connected to either one or two LI-COR LI-7000 gas analyzers to measure CO2. An in situ “field calibration” method, that uses four calibration gases with an uncertainty on the order of ±0.1 μmol mol−1 relative to the WMO CO2 mole fraction scale, revealed CO2 output from the LI-7000 had a slightly nonlinear relationship relative to the CO2 concentration of the calibration gases. The sensitivity of the field-calibrated CO2 to different forms of the field-calibration equation is investigated. To evaluate TGaMS performance, CO2 from collocated inlets, portable gas cylinders, and nearby independent CO2 instruments are compared. Results are as follows: 1) CO2 measurements from HYDRA multiple inlets are feasible with a reproducibility of ±0.4 μmol mol−1 (based on the standard deviation of the CO2 difference between collocated inlets when HYDRA was operating with two LI-7000s); 2) CO2 differences among the various field-calibration equations were on the order of ±0.3 μmol mol−1; and 3) comparison of midday hourly CO2 measurements at 30 m AGL between TGaMS and an independent high-accuracy CO2 measurement system (within 300 m of TGaMS) had a median difference and standard deviation of 0.04 ± 0.81 μmol mol−1 over two months.

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