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The Profiling Reflectance Radiometer (PRR) is an optical instrument designed to make profiles of downwelling irradiance and upwelling radiance through the upper 200 m of the water column. Simultaneous to these profile measurements (using the PRR-600), reference downwelling irradiance measurements are also made at the sea surface using a sister instrument (the PRR-610). The data from this reference instrument can then be used to normalize the profiled measurements to the incident irradiance. The PRR instruments used have sensors at wavebands with the following center wavelengths:
412, 443, 490, 510, 555, and 665 nm
Each of these wavebands have bandpasses of approximately 10 nm. In addition to these bands, the PRR-600 used also measures PAR (400-700 nm), natural fluorescence, temperature and depth, and the PRR-610 also measures PAR. Tilt and roll sensors were added to the PRR-600 in September 1998. The sampling frequency is approximately 2-3 Hz. Profiles of photosynthetically available radiation (PAR) and PAR attenuation coefficient (KPAR) measured using the PRR-600 are shown in the bottom panels of the figures below. Due to the tendency for the instrument to tilt back-and-forth when brought up through the water column, only the downcast profiles are included.
Figure 58 shows a time-series of the 1% light level and KPAR during the 9 years we've been collecting PRR data. Both vary seasonally. The average 1% light-level at Station ALOHA is about 106 m while the average KPAR between 100 & 150m is 0.0439 m-1. Downwelling irradiance measured during the Primary Production incubation period is shown in Table xxx. The results compare favorably with the integrals obtained using the LICOR LI-1000 which also measures PAR. This study is a collaborative effort between the College of Oceanic and Atmospheric Sciences of Oregon State University and the Laboratory for Microbial Oceanography of the University of Hawai'i at Manoa. | |||||
