The Oklahoma Atmospheric Surface-layer Instrumentation System (OASIS) Project is a National Science Foundation experiment designed to estimate the surface energy budget at approximately 90 Mesonet sites statewide. Each remote Mesonet station is fully automated with routine maintenance performed two or three times per year. Thus to close the energy budget, net radiation has to be measured accurately over periods of time with minimum instrument maintenance. Unfortunately, most net radiation sensors require weekly cleaning and regular replacement of the polyethylene domes. In addition, some radiation sensors require ventilation to minimize convective currents within the dome.
The Kipp & Zonen NR-Lite claims to be among the first modern radiation sensors which does not require the use of domes, thereby reducing maintenance requirements. The NR-Lite is a simple thermopile detector with a teflon-coated, cone-shaped surface. The surface is cone-shaped to improve the cosine response function. The black teflon coating allows the sensor to remain relatively clean.
The OASIS Project evaluated the NR-Lite model for eight months to test its accuracy, reliability, and durability. A field intercomparison site was built near the Norman Mesonet station. Seven Kipp & Zonen NR-Lites, a Radiation Energy Balance Systems (REBS) Q7, a Kipp & Zonen 4-way CNR1, and a 4-component Eppley system were compared. Each instrument was mounted 1 m apart at a height of 3 m over similar vegetation cover. Data were collected in real-time every minute.
Results from the intercomparison reveal a relatively accurate and robust sensor for most meteorological applications. Nevertheless, net radiation errors were detected due to possible miscalibration, wind speed effects, and noncosine response. Some problems were found to be common to all sensors tested, however. The presence of rain, dew, or frost inhibited accurate radiation measurements in most cases.