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Remote Research & Measurement Co., 214 Euclid Av., Seattle WA 98122, 206-420-7061 info@rmrco.com


The RAD (Radiation Analog to Digital Interface) with Eppley PSP and PIR was installed on the R/V Pisces (pdf 2.5 MB) on Friday 15 Jan 2010. Michael Reynolds of RMR Co. made the installation with assistance from Tim Barnes (Integrated Electronics Technologies, Inc.), Tim Burrell (NOAA), and Robert Carter (NOAA, SCS engineer). The installation was the third NOAA vessel to receive a RAD and more are scheduled to receive system as they come on line.

The RAD was placed in an exposed location at the stern of the ship. This has the advantage of having an excellent unobstructed view of the sky. Often the ship mast and other superstructure will cause shading and infrared contamination. Also, this location is easily reached by a technician so the glass domes can be easily cleaned on a regular basis. However, the disadvantage of this location is that it is downwind from the exhaust stacks. The stacks are well ahead of the location and well above and directed outboard to port. The engines are new and have low emission. It may be that contamination to the domes will be minimal. However the condition of the domes will be watched carefully and they will be cleaned regularly.

The RAD (Radiation Analog to Digital interface) was designed to solve a difficult problem for climate-quality data stations. Radiation sensors, both longwave, infrared, sensors and shortwave, solar, sensors use thermopiles to sense incoming radiation. In the case of the longwave sensor the temperature of the sensor case and dome must be measured as well. The thermopile output is measured in microvolts. The calculation of actual radiation, in units of watts per square meter (W/m^2) requires good sensor calibration and, in the case of longwave measurements, the computation is a reasonably complex function of the thermopile output and the various sensor temperatures.

Scientists generally want real time data in physical units and with radiometers this is usually not possible. Having physical units is crucial in assessing measurement accuracy or diagnosing faulty equipment.

RAD is a small but powerful computer that connects to the longwave and shortwave sensors. The Eppley Laboratory standard sensors are used in these initial designs. Basically the RAD consists of very high precision, high gain preamplifiers, a 16 bit analog-to-digital-converter (ADC), and a powerful microprocessor. The microprocessor, an AVR chip, is programmed in C to sample all channels, eliminate noisy samples, average for selected times, and transmit a NMEA-like text data string over an RS232 serial connection. The Pisces operated at 9600 baud over a 75 m cable. A considerable amount of attention to grounding, filtering, digital sampling has yielded a device with exceptionally low noise (± 0.02%). The operator can enter calibrations, offsets, time, and sampling rates over the serial connection through a simple menu.

A graph from the SCS showing the longwave flux (PIR) and the shortwave flux (PSP) signal over about an hour. The longwave flux, in W/m^2, slowly increases from 340 to 350 over the time period. This reflects increased cloudiness and increased infrared from the low cloud. The solar flux, also called shortwave or visible radiation, is a low value of 250 W/m^2 and decreases to 200. This too reflects an increase in cloudiness. The two signals are exceptionally clean of noise effects.