| Summary: | These folders contain .csv files of lake water temperature time series collected during the period April to August. Data collected at the same locations using the same configuration will be found in the yearly files, where the year is defined as that year when the data were downloaded. At the first subfolder level, the lakes are differentiated by the Eastern and Western Transects; see accompanying jpg image (CALON_sites_overview.jpg) and list of Lake Float Locations. The instrumentation configuration is identical in most cases. Generally, a rope is attached to an anchor. The other end of the rope is attached to a float. An Onset computer U12-015 water temperature data logger is affixed to the rope 30 cm below the float. Another data logger (U20) is attached to the surface on an anchor resting flat on the lake bed. The U20 is a water level/water temperature logger, so records the change in the water depth over the period of record. The water level is calibrated and corrected using the barometric pressure record from the nearest terrestrial met station. This is done in the Onset Hoboware software. All sensor specifications are shown below. In April, a 10" diameter hole is augured through the ice and the instrument string is lowered to the lake bottom with the buoy sitting on the surface of the ice. It should be noted that there is often some movement of the floats that get entrained by the moving ice slab in spring or by strong wave activity in summer. All loggers record hourly measurements on the hour using Alaska Standard Time (AST). In each data file, column headings are Time_AST, LakeDepth_m, TempBed_C (at corresponding lake depth), and TempSurface_C. Prior to deployment all loggers were tested in a chamber circulating ethylene glycol at temperatures of 0, 5, 10, 15, 20 degrees C and calibration coefficients were determined from these test for each sensor. After sensor downloads, data records were corrected using these calibration models. Pressure transducer water level loggers were calibrated in a similar manner and corrected accordingly. In a few cases, additional sensor strings were deployed at a different location in the same lake. This typically occurred when the lake was especially deep (>4 m), and was designed to obtain measurements of the entire water column. In these cases, an Onset Computer U23 water temperature logger was used. These data are shown as additional columns in the .csv files. Finally, there are also some stand alone files for a few select lakes ("focus lakes") that report time series of water quality including dissolved oxygen and conductivity. Loggers were manufactured by Onset Computer; Hobo U24-001 for conductivity and U26-001 for the dissolved oxygen (see specs in readme). These loggers were attached to the base of the instrument string described below for a few lakes. Loggers are deployed in August, recovered the following August, serviced, and redeployed. Measurements are collected hourly.
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