Accurate underwater spectral measurements needed for vertical light profiling, primary productivity studies, and many other applications can be easily collected using the LI1800UW Underwater Spectroradiometer. The LI1800UW features a precision optical package and an internal microcomputer in a waterproof housing that allows measurements to 200 meters in depth.

Compact Oprics
The key to the LI-1800UW is a compact optical system which combines a holographic grating monochromator, an order sorting filter wheel, and a stable, high quantum efficiency silicon detector to provide a wide dynamic measurement range and a mid-band noise level typically below 0.01% of surface irradiance. The wavelength range for scanning is 300-850nm and wavelength drive intervals are 1, 2, 5, or 10nm. With scan speeds ranging from 20-45nm per second, a scan from 400-700 in 2nm steps takes just 10 seconds (scan speed varies with wavelength drive interval).

Internal Microcomputer
The internal microcomputer of the LI-1800UW controls all operations which includes scanning and the collection, reduction, storage and output of data. Scanning can be initiated from the surface by a single command from the 1800UW-O1B Portable LCD Terminal. For each scan, the user can specify the wavelength limits, wavelength drive intervals, and the number of scans to average. Scan averaging is useful under conditions of fluctuating radiation, such as those resulting from waves or atmospheric conditions in near surface measurements. The LI-1800UW can be programmed for unattended operation during which it will 'wake-up", take a scan, and store the data at a user specified time interval. This is particularly useful for studies involving benthic communities since the LI-1800UW can be submersed in the benthos and retrieved after collecting a number of scans. Data Storage After each scan, the spectral data are automatically corrected for the immersion effect (wavelength dependent) and are then stored in the LI-1800UW's internal memory. Each data file also contains a header that lists the date, time, scan parameters, and user remarks. With up to 512K bytes RAM for data storage, over 1000 scans can be stored in the 400-700nm wavelength range.

Data Communication
Communication with, the LI-1800UW is normally accomplished using the 1800UW-O1B Portable Terminal. The 1800UW-O1B is a 2 line LCD terminal with a membrane keyboard for operation in harsh environments. The circuitry needed for charging the LI-1800UW with AC power is also contained in the 1800UW-O1B. In the field, an IBM PC compatible laptop computer can be used to communicate with the LI-1800UW and retrieve data while the LI-1800UW is still underwater. Software is available (model 1800-14) which acts as a terminal emulator for data communication, and also provides functions for data reduction and storage. The 1800-14 software is frequently used to plot spectral irradiance or spectral photon distribution at a variety of depths. The LI-1800UW also has a number of built-in data reduction and output commands which allow the user to integrate over the wavelength limits selected (in quantum or energy units), calculate photo-synthetic photon flux density, plot a data file on the 6000-03B Plotter/Printer, and more.

Measurements in Air
Although the LI-l800UW is designed for measurements underwater, it is also calibrated for use as a terrestrial spectro-radiometer. The LI-1800UW can be used in air with the standard 1800 cosine collector, or with any of the optical receptors available for the LI-1800 Portable Spectroradiometer.