Summer Leads Data CONTACT INFORMATION: P.I.s Clayton Paulson and W. Scott Pegau COAS 104 Ocean Admin Bldg Corvallis OR 97331 phone: 541 737-3504 fax : 541 737-2064 email: cpaulson@oce.orst.edu spegau@oce.orst.edu DATA VERSION: The data was initially processed by W. Scott Pegau in August of 1999. The data supplied is version 1. This data is in a preliminary format. Darks and calibrations have been applied. The data needs to be compared to the meteorological data to identify if there are times when the radiometers were tilted. This is most likely to have occurred in June when the radiometer supports were mounted to the ice. In July we began using one of our boats as the radiometer support. This document contains notes on the collection and processing of data related to the Epply radiometers used to make surface measurements as part of the summer leads portion of SHEBA. Further information and pictures of the equipment is available at http://photon.oce.orst.edu/ocean/projects/sheba/sheba.htm All of the data was collected from a small lead about 1 km WNW from the ship. EQUIPMENT: These measurements were made with two Epply radiometers a PSP (#29097) and a Model 8-48 black and white pyranometer (#11848). The PSP was calibrated with the other PSP sensors used at SHEBA prior to deployment in the Arctic. The pyranometer was intercalibrated with the PSP at the beginning and end of our deployment. The data was logged using a Cambell Scientific data logger. Samples were collected every 30 seconds. The sampling periods generally lasted 1 day. Several mounting arrangements were used. Early on we had a frame that was attached to the ice. It held the radiometers approximately 1.5 m from the ice edge and about 1 m above the water. By mid June we had problems with the frame anchoring system melting out so we attached the frame to a spare boat, which was then placed next to the ice edge. The end result put the sensors about 1.5 m from the edge and 1 m above the water. By mid July an ice shelf had formed and to get the radiometers beyond this shelf the boat was launched. In this case the radiometers were only about .4 m above the water. Ice rime was a problem throughout our measurement period. PROCESSING NOTES: Instrument dark values were determined by covering each sensor with several layers of black felt cloth and recording the instrument output. This was done on one occasion, June 15. To provide a calibration for the black and white pyranometer both sensors were placed side by side measuring downwelling irradiance. A linear regression of the two output voltages with the darks subtracted provided a correction slope for the pyronometer. This was done on June 10 and August 3 and the scaling factor from the June 10 measurements was applied to all data. The August 3 data showed no apparent drift between the sensors over time. After applying the linear scaling factor the two sensors agreed within 5 W/m^2. The downwelling irradiance was determined by subtracting the dark value from the measured PSP voltage and then multiplying by calibration factor. The upwelling irradiance was determined by subtracting the dark value associated with the pyronometer voltage, multiplying by the intercalibration scaling factor, and then multiplying by the PSP calibration factor. The albedo was calculated as the upwelling irradiance divided by the downwelling irradiance. DATA FORMAT: The data is supplied in ascii, tab-delimited, columnar format files. Each file covers a sampling period of about a day in length. The columns include the date as YYYYMMDDHHmmss, the julian date with January 1 being day 1, downwelling irradiance, upwelling irradiance, and albedo. The irradiance values are in W/m^2 and albedo is a unitless parameter. LOG: Our complete field logbook is available through our web page http://photon.oce.orst.edu/ocean/projects/sheba/results.htm the notes below provide pertinent information to these measurements only Date Comments 06071998 over water 06101998 side-by-side comparison 06111998 deployed on the boat, some ice formed on the PSP 06121998 ice anchor melting out the frame is at an angle 06151998 radiometer dark values measured, framework melting out 06171998 on wooden framework 06181998 set up on boat 06191998 on boat 06211998 on boat, on ice, over skim ice 06231998 on boat, on ice, over water, ice formed on PSP, ice formed on lead 06291998 on boat, on ice, over water 07031998 on boat, on ice, over water 07071998 on boat, on ice, over water, ice shelf ~ 1m wide, rain on insts. 07081998 on boat, on ice, over water 07091998 on boat, on ice, over ice shelf 07101998 on boat, on water, over water, moved the boat onto the ice while away for lunch, lots of little ice bits around 07141998 on boat, on ice, over water, moved to another location on boat, on water, over water 07171998 on boat, on ice, over water, CTD attached to the boom for time series 07231998 on boat, on ice, over water, CTD attached to the boom for time series 07301998 over a meltpond with some slush ice accumulating, no slush left by early afternoon, radiometers icing up 07311998 over a meltpond with some slush ice accumulating 08031998 side-by-side comparison