Relative surface artificial light at night map under clear skies of Lake Washington, Lake Sammamish, Sammamish Slough and the Ship Canal, WA

This data is a measurement of relative light level along shorelines and pelagic habitat of Lake Washington, Lake Sammamish, Sammamish Slough and the Lake Washington Ship Canal. The data was collected at true night (between the end and beginning of astronomical twilight) under clear sky conditions. The light sensor was mounted on the roof or surface of water vessels. Nearshore data and Sammamish Slough sampling utilized kayaks while all other transects were conducted from small motorized vessels. The relative light measurements were collected with a Wildlife Computers TDR-Mk9 sensor. This sensor measures in relative units on a log scale and is sensitive to light between 380-460nm. Mk9 light data was recorded each second with light "anomalies" such as lights from a passing boat or headlamp were removed. Light data is synced with location data from Garmin handheld devices. Inter-Mk9 calibration was conducted using a standard light source with two intensities. The calibrated results are published. These data include an averaged shapefile within 500m pixel areas and a file with the vector information with light level and location data.