----------------------------------------------------- Metadata for UAF Sea Ice Mass Balance Site 2008 ----------------------------------------------------- Revision: 27 Feb 2009 Chris Petrich chris.petrich@gi.alaska.edu (Field Work) Daniel Pringle daniel.pringle@gi.alaska.edu (Data Processing) BRW08_MBS_all.txt -ascii -tabs ----------------------------------------------------- In 2008, the site was about 1000 meters offshore of Niksuiraq, the hook at the end of the road out to Pt. Barrow. Site installed by Chris Petirch, Jonas Karlsson. GPS location: (71° 21' 56.45" N, 156° 32' 39.01" W) The following measurements are recorded: (i) snow and ice thickness and local sea level; (ii) temperature profile through air-snow-ice-water; (iii) air temperature and relative humidity at 2m above the ice. Hydraprobe dielectric measurements were not made this year. The code was written for 3 snow pingers. 1 Campbell SR50 was installed intially, with two more (SR50 + SR50a) to be added during spring/ summer melt season to look at ice surface ablation and pond drainage. Mass Balance Site: Campbell CR10X Data logger, AM1664 multiplexer, SM4M storage module, SC32A adaptor. FreeWave Spread-spectrum, no-license radio: FGR 115-WC, 900 MHz Bluewave 10 dB directional Yagi Antenna (BMY890K). Campbell SR50 Sonic Ranger (snow pinger) with hardware-set SDI address = 0. SR50 + SR50a to be added in melt season (with hardware-set SDI addresses = 1,2) Shielded 107 air temperature probe, Benthos underwater acoustic altimeter PSA-916 (one upward looking, one downward looking), CRREL-design thermistor strings (3 x 1 meter sections), Batteries: 2 (of 4 total) UAF 12V cells currently stored at BASC (85 Amp-hr Exide). BASC Site: Bluewave 10 dB omni-directional Antenna and RF coaxial cabling to: FreeWave Spread-spectrum, no-license radio: FGR 115-RC, 900 MHz, connected to the serial port of a dedicated control PC with an internet connection. ----------------------------------------------------- Measurement intervals: The measurement interval was originally 15 minutes, and not changed this year (2008) Logger times (col 1 and 4) are in Barrow local time. Prior to April 9, this is Alaska Standard Time = UTC - 9 Logger time changed to AK Daylight savings time at 11:12 am, April 9. Note jump from 10am to 11:15 am. ----------------------------------------------------- Listed below are examples of the entries in each column in the data files. Notes: (i) All depths are referenced to the ice/water interface at the time of installation. (ii) T107 water temp is used by the data logger program to calculate the underwater depths using c(S,T). An offset of -0.45 C was added to T measured, based on lab tests in a snow/ ice water bath. (iii) Similarly, the snow pinger uses a correction from the air temperature measurement, vs,air = .. (This shielded sensor at 2.25 m above ice/snow interface bottoms out at – 39.67 C). (iv) Time* is the time as day of year in a decimal format, here 11:00 am on day 75 (March 16, 2006 ) gives 75.45833 (v)The reference resistor is a low-temperature co-efficient resistor. Its variability indicates the noise in the temperature measurements. ----------------------------------------------------- Events: April: Snow pinger SR50(0) was replaced with SR50(1) on April 12 (DOY 103). SR(0) was malfucntioning - returning intermittent data and zeroes. The online data processing was changed on April 14. March: A Polar bear collapsed the tower with downward looking snow pinger and CS500 air temp + humidity probe in early March (day 70) shortly after the battery failed. The site came back on line with new batteries on day 74, with the tower still collapsed. It was repaired by CP the following week with all original cables and sensors retained. June: Melt season poingers installed on day 149 (May 28) by Hajo Eicken. At this point, mast pinger was set to address 2. New pingers were: (1)(new model, SR50A) approx. 7 m from the logger box at a height of 70 cm above the snow surface. Initial snow depth 5 cm; spot chosen to hopefully turn into a pond. (2)(old model, SR50 - previously malunctioned but we'll try again..) installed roughly 15 m away from the logger box at a height of 50 cm above the snow surface. Snow depth was 12 cm. ----------------------------------------------------- Quality Comments: These data have been processed to compute the physical values from the measured quantities. Periods of 'bad' data have been removed. However the time-series is not complete due to battery failure, and intermittent 'bad' values are returned. NOTE: Plotting time-series as points not lines at least during inspection is recommended. Data gaps : DOY 70.5 - 74.5 (March 10 -14) due to battery failure DOY 128.9 - 129.45 (May 7 - 8) unknown, not battery swap (?) Temperature measurements: Badly-behaved (short circuit due to leak?) thermistors: String 2, therm 1 (50 cm below initial ice/snow interface), String 3, therms 6,8 (both in water throughout). NB: THESE DATA ARE LEFT IN DATASET. REMOVE FOR ANALYSIS. No absolute calibration of T107 water sensor or thermistor strings. Therms in water give offsets of approximately +/- 0.1 C. Resolution of the CR10X system in temperature measurements can be inferred from equivalent temperature of the standard resistor (on CR10X panel in place of upper most thermistor (50 cm above ice). This gives mean and standatrd dev. throughout season of -5.894 (0.005) C. The maximum variability is approx +/- 0.012 C. Underwater sounders: These return "99" when a sufficeintly strong return signal is not detected. After postprocessing for pinger positions, these values appear as approx. +103 and - 97. THESE DATA LEFT IN. Snow pingers: The original SR50 pinger had some problems. Odd values are sprinkeld throughout season, especailly between bear attack and replacement on April 12 (Day 103). Looks like some good data here but many no-detect measurements. Then shifts later in the season due to the mast slipping through rotten ice. Corrections were made for mast slippage of 7 cm at Day 162.64, and 15 cm at Day 164.6. NOTE ADDED 27 Feb 2009 (CP): THE VERTICAL MAST POSITION IS NOT ADJUSTED PROPERLY DURING SURFACE ABLATION (approx. day 158 onwards). HENCE, THE SNOW DEPTH LISTED IN THE DATA FILE IN COLUMN 10 IS WRONG STARTING APPROX. DAY 158; REFER TO COLUMN 12 FOR SURFACE ABLATION. STARTING APPROX. DAY 160, THE SUM OF COLUMNS 10 AND 13 IS THE TOTAL ICE THICKNESS. The melt season pingers (our first season doing this) suffered problems due to leaning-over in the melting ice. This would cause an increase in the apparent snow depth. Pingers (cols 10:12) value set to zero when either not conencted (ie. before melt season pingers installed) or when no signal detected and an error returned. ----------------------------------------------------- Column Description 1 Time* (decimal) 2 year 3 day 4 time (hhmm) 5 logger temp [C] 6 bat volts [V] 7 T107 water temp [C] 8 CS500 rel hum [%] 9 SC500 air temp [C] 10 snow depth MAST [m] 11 snow depth SR50 [m](melt season, intermittent) 12 snow depth SR50A[m](melt season) 13 ice thickness [m] 14 sea level [m] 15 Ref. res. equiv.temp[C] 16 T1 (+ 40 cm) [C] 17 T2 (+ 30 cm) [C] …… … … 25 T10 (- 50 cm) [C] BAD …… … … 40 T25 (-200 cm) [C] BAD 42 T27 (-220 cm) [C] BAD …… … … 44 T29 (-240 cm) [C]