These are both research-grade net radiometers that measure the energy balance between incoming short-wave and long-wave infrared radiation versus surface-reflected short-wave and outgoing long-wave infrared radiation. The net radiometers, however, are produced by different manufacturers. The CNR4-L is manufactured by Kipp & Zonen. The NR01-L is manufactured by Hukseflux.
The specifications of the CNR4-L and NR01-L are very similar. For regular field use, the small differences between the two net radiometers may not be significant. One notable difference, however, is that the NR01-L includes a 1 W heater that minimizes the formation of dew and melts frost.