Taconite Inlet Project



4. Data acquisition/procedures

All regular interval meteorological measurements at the weather station were made by Campbell Scientific, Inc. (CSI) model 21X microloggers. These are DC-powered, microcomputer-based dataloggers containing a set of pre-programmed instructions on two applications Programmable Read Only Memory (PROM) chips. The user can draw from these instructions to create flexible measurement and processing programs.

The measurement of individual sensors was done every 60 seconds, with few exceptions. The measurements were then numerically processed by the micrologger, involving procedures such as scaling to physical units (e.g. millivolts to Wm^-2), linearization of nonlinear sensor signals (e.g. thermistors), and computing derived values from measured variables prior to averaging (essential for nonlinear relationships such as vapor pressure from temperature and RH). Values measured by the micrologger could be scanned manually at any time, to insure the instruments were functioning. Data processed by the micrologger were internally stored in random access memory (RAM), also according to user-programmed instructions.

Data were retrieved from the microloggers in both hard copy and magnetic form. Double and triple redundancy was practiced, due to the harsh environmental conditions at, and returning from, Taconite Inlet. One set of data was retrieved with a small battery powered printer (CSI model CR56), which was heavy and slow but provided insurance against loss of data stored in magnetic form. The meteorological data collected in 1991 were stored on cassette tape (CSI model RC35 recorder) and retrieved using a CSI C20 Cassette - Computer Interface, a short batch program written in Basic, and CSI PC208 software; this system was reliable, yet slow and somewhat cumbersome. For example, data could only be dumped from the micrologger to the cassette recorder at temperatures above freezing, and the C20 Interface required AC power. In 1992, the data were acquired directly from the microloggers by a notebook computer, using a CSI SC32A RS-232 Interface and CSI PC208 software (Telcom). This method was very fast and reliable, and data could be inspected immediately. In general, notes were made throughout each field season about any sensor or program adjustments.

The time used for all measurements, except as noted for 1992 radiation measurements, was Local Standard Time (LST). At Taconite Inlet, the Pertinent Standard Meridian was 75° , which is within the Eastern Standard Time Zone (GMT - 5 hours). Standard time was used, rather than Daylight Savings Time, because Canadian Atmospheric Environment Service (AES) weather stations, including Alert, Eureka and Resolute, operate on LST. These stations are in Atlantic, Eastern and Central time zones, respectively.


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