--------------------------------------------------------- Metadata for UAF Sea Ice Mass Balance Probe 2009 --------------------------------------------------------- Version: 25 June, 2009 Chris Petrich chris.petrich@gi.alaska.edu Data file name: BRW09_MBS_all.txt Format: ASCII, columns delimited by TAB, rows delimited by LF ----------------------------------------------------- Changes: -------- Jun 25: condition of probe after removal Jun 25: sliding pinger mast Mar 30: additional snow pinger (ID=0) Mar 27: added specs of wind turbine Mar 9: updated events Feb 17: updated quality and events section Feb 13: updated events Feb 9: update of Notes (ii) and (iii): temperature offsets (mention application of wrong temperature offset in data logger program) ----------------------------------------------------- In 2009, the site was about 1000 meters offshore of Niksuiraq, the hook at the end of the road out to Pt. Barrow. The site was installed by Chris Petirch, Matthew Druckenmiller, and Jeremy Harbeck. GPS location of data logger: 71.36655 deg N, 156.54140 deg W The following measurements are recorded: (i) snow depth, ice thickness, and local water depth; (ii) temperature profile through air-snow-ice-water; (iii) air temperature and relative humidity approx. 2m above the ice. The mass balance site was installed 15 January 2009 with one snow depth pinger mounted at temperature/humidity mast above the upward looking altimeter. (Campbell SR50, address 0; replaced on 24 January with Campbell SR50, address 2. The new instrument started to deliver data at 13:45 AKST.) Thermistor string, data logger box w/antenna, and mass balance mast are collinear with approx. 5 m separation between each. On March 28, an additional snow pinger SR50A was added (ID=0). Another additional snow pinger (Campbell SR50a) was expected to be deployed but was never deployed. The thermistor string was removed on 12 June 2009 (the ice was completely melted around the string since at least 9 June); the remaining sensors were recovered on 13 June 2009 by Chris Petrich and Josh Jones. Mass Balance Site: Campbell CR10X Data logger, AM1664 multiplexer, SM4M data storage module, SC32A adaptor FreeWave Spread-spectrum, no-license radio: FGR 115-WC, 900 MHz [set to slave mode] Bluewave 10 dB directional Yagi Antenna (BMY890K) Campbell SR50 Sonic Ranger (snow pinger) with hardware-set SDI address = 2. Campbell SR50A Sonic Ranger (snow pinger) with hardware-set SDI address = 0. A second SR50a was not added (with hardware-set SDI addresses = 1) Shielded Campbell T107 air temperature/humidity probe Benthos underwater acoustic altimeter PSA-916 (one upward looking, one downward looking), Underwater thermistor, Campbell CS500, mounted next to Benthos altimeters CRREL-design thermistor strings (3 x 1 meter sections), (10 cm thermistor spacing) Batteries: 2 (of 4 total) UAF 12V cells currently stored at BASC (85 Amp-hr Exide). Wind turbine: (installed 26 March pm, local time) Aero4Gen 12V, 100 W max. LVM4SB12-T temperature compensated charge controller, connected in parallel to the batteries BASC Site: Bluewave 10 dB omni-directional Antenna and RF coaxial cabling to: FreeWave Spread-spectrum, no-license radio: FGR 115-RC, 900 MHz [set to master mode] connected to the serial port of a dedicated control PC with an internet connection. Communication with Campbell LoggerNet 3.5.1 ----------------------------------------------------- Measurement intervals: The measurement interval was 15 minutes. Values reported are instantaneous, non-averaged measurements. The data logger clock was set to Alaska Standard Time (UTC-9). However, times reported below are converted to UTC. ----------------------------------------------------- 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 correct the underwater depths delivered by sounders using an equation for the speed of sound as function of temperature. The T107 temperature is read, an offset of +0.45 C is applied, and the speed of sound is calculated. This is bogus. The calculated temperature is in the range of -1.5 C, while it should be -1.9+-0.1 C. TODO: correct data logger program. Expected error in ice thickness and water depth measurement: < 5 mm. The temperature reported in this data file (column 7) is back-corrected by applying an offset of -0.45 C. (iii) Similarly, the snow pinger uses a correction from the air temperature measurement of the CS500. No temperature offset is added. (The operating temperature of the CS500 is down to -40C. The lowest reading returned by the temperature sensor is –39.66 C. The sensor does not return a special code for "out of range".) (iv) Day-of-year is the fractional day of the year with midnight 1 January midnight being 1.0. (v) The reference resistor is a low-temperature co-efficient resistor. It replaces the upper-most thermistor of the CRREL thermistor string. Its value is close to the resistor in the voltage bridge. (vi) Data from the the relative humidity sensor are questionable. Sensor needs replacement. ----------------------------------------------------- Events (local time, Alaska): 03 June: Pinger mast starts to slip vertically through the ice. 28 March: Installed snow pinger SR50A with SID=0. 26 March: Installed Aero4Gen wind turbine and charge controller, both connected in parallel to the batteries. First measurement on day 86, 02:15 UTC reading about 14.5 V at 15 mph wind and -23 C air temperature. 08 March: Alaska changes to daylight savings time at 2 am Alaska Standard Time. This should not affect the data file. 04 March: Batteries replaced by BASC staff on day 64, 02:30 UTC. No measurements at day 64, 02:30 UTC. 01 March: Batteries recover enough for operation by themselves. 27 February: Batteries drained: Starting day 58, 09:30 UTC the battery voltage drops from 11.20 V to 10.54 V at day 58, 18:45 UTC. The next measurement recorded is day 60, 21:45 UTC at 11.66 V. 11 February: 11:30 AKST bear bends up snow pinger arm (between 20:30 and 20:45 on day 42, UTC) apparent distance between pinger and snow increases 96 mm. Data in the file have correction +0.096 m applied. 09--12 February: Air temperature may have fallen below -40 C. 08 February: Battery change by BASC staff (data logger generates second entry with same time stamp) 24 January: Replacement of SR50 snow pinger (ID=0) with another SR50 snow pinger (ID=2) by BASC staff 15 January: Installation of air temperature/humidity probe and SR50 snow pinger (ID=0) 14 January: Installation of thermistor string, data logger box, antenna, and underwater sounders ----------------------------------------------------- Quality Comments: The data have been processed to compute the physical values from the measured quantities. Missing values or invalid data are indicated as -9999. Thermistor string temperature measurements: (Note: the upper and middle sections are swapped with respect to previous years.) Two bad thermistors in string 3 (bottom), data masked by -9999. The thermistor string is completely embedded in conduit painted white. It is subject to solar radiative heating. Effects due to thermal conductivity, and the effective response time are unknown. No calibration of thermistor strings. Thermistors in water have individual offsets of approximately +/- 0.1 C. The thermistor string was melted out, i.e. surrounded by water rather than ice, since 9 June. Post-deployment inspection: protective coating was missing from thermistor T18 (second to last in middle string). Protective coating of thermistors T15 and T17 were lose or cracked. (Sealed these flaws with PC-Marine hand moldable expoxy putty for next year.) Crude absolute calibration of T107 water sensor (offset -0.45 C added). Underwater sounders: Return values of "99" (indicating missing return signals) and values indicating grossly wrong distances are flagged as -9999 Sounder measuring ice thickness shows periodically an increase in path length by approx. 2 cm (this looks like noice with ice thicknesses that are too thin). These periods seem to be related to changes in the environment and may indicate actual changes in the acoustical path length. The pinger mast started to slip vertically on June 3. Hence, measurements of snow depth (column 12), ice thickness (column 13) and water depth (column 14) are systematically biased since June 3 inclusive. Note that water depth is referenced to the ice--water interface. Ice grew 0.7 m since deployment, equivalent to a change in freeboard of several centimeters. This needs to be accounted for. Post-deployment inspection: sensor of upward-looking sounder was coated by a thin film of algae; sensor of downward looking sounder was free of algae. Water was a soup of brown/green algae in mid June. Snow pingers: The original SR50 pinger (ID=0; column 12) had problems, returning "0" readings most of the time (indicated as -9999 in the data file). The intermittend readings are considered good. The snow pinger on the mast has an offset of +0.096 m applied starting day 42, 20:45 UTC. This is to compensate for misalignment of the temperature/pinger arm after a bear visit. Pingers (columns 10 to 12) have value set to -9999 when either not connected (i.e. before they were installed), when no signal detected (99 returned), or when distances measured were obviously wrong (raw data <0.5 m or >5 m). The pinger mast started to slip vertically on June 3. Hence, measurements of snow depth (column 12), ice thickness (column 13) and water depth (column 14) are systematically biased since June 3 inclusive. Snow depth/surface ablation determined by the pinger in column 10 is considered reliable. Distance measurement of the pinger agreed with tape measure to better than 0.01 m on 13 June. Time: Since I was not able to reliably determine a systematic drift of the data logger clock between mid Feb and mid June based on time stamps attached by the processing computers, the clock of the CR10X is probably accurate to better than 5 minutes throughout the course of the field season. ----------------------------------------------------- Column Description 1 day-of-year in UTC (decimal fraction) 2 year 3 day of the year in UTC (non-fractional) 4 time (HHMM) in UTC 5 internal data logger temp (deg C) 6 battery voltage (V) 7 T107 water temp (deg C) 8 CS500 rel hum (%) 9 CS500 air temp (C) 10 snow depth from SR50a with ID=0 (m) (deployed 28 March) 11 snow depth from SR50a with ID=1 (m) (never deployed, always -9999) 12 snow depth from SR50 at the MAST (m) (either ID=0 or ID=2) *** do not use column 12 uncorrected after 2 June *** 13 ice thickness (m) *** do not use column 13 uncorrected after 2 June *** 14 water depth plus freeboard (m) *** do not use column 14 uncorrected after 2 June *** 15 Reference resistor equivalent temperature (C) (reading should be constant) 16 T1 (+ 40 cm) (deg C) 17 T2 (+ 30 cm) (deg C) .... 20 T5 ( 0 cm) (deg C) -- nominal ice--snow interface .... 24 T9 (- 40 cm) (deg C) -- last thermistor of top string 25 T10 (- 50 cm) (deg C) -- first thermistor of middle string .... 30 T15 (-100 cm) (deg C) (see comments) .... 32 T17 (-120 cm) (deg C) (see comments) 33 T18 (-130 cm) (deg C) (see comments) 34 T19 (-140 cm) (deg C) -- last thermistor of middle string 35 T20 (-150 cm) (deg C) -- first thermistor of bottom string .... 38 T23 (-180 cm) (deg C) (questionable since mid April) .... 40 T25 (-200 cm) (deg C) (bad, always -9999) .... 42 T27 (-220 cm) (deg C) (bad, always -9999) .... 44 T29 (-240 cm) (deg C)