============================================================== Metadata file for SIZONet mass balance probe, Barrow, AK, 2011 ============================================================== .. This document uses reStructuredText markup. See http://docutils.sourceforge.net/rst.html for details. .. footer:: SIZONet Mass Balance Metadata, Barrow 2011 .. |deg| unicode:: U+000B0 .. DEGREE SIGN .. |times| unicode:: U+000D7 .. MULTIPLICATION SIGN .. |degC| replace:: |deg|\ C .. |Ohm| unicode:: U+02126 .. OHM SYMBOL .. |PM| unicode:: U+000B1 .. PLUS-MINUS SIGN .. |dash| unicode:: U+02013 .. N-DASH .. |ice-snow| replace:: ice\ |dash|\ snow .. |^3| replace:: :sup:`3` :Revision Date: 8 June 2011 :Author: Chris Petrich, ``chris.petrich@gi.alaska.edu`` .. contents:: Revision History ================ 8 Jun 2011: update on probe recovery, errors 29 May 2011: update on SR50A outage and Benthos distance measurements 3 Apr 2011: update on CS500 errors, wind turbine dump resistor 22 Feb 2011: update on status of 107-L (Errors) 1 Feb 2011: document creation Overview ======== Date of deployment (season 2010/11): 24 January 2011 Date of recovery: 7 June 2011 Location: * Chukchi Sea, landfast ice between Niksuiraq and Point Barrow, Alaska * 71.366885\ |deg| North, 156.545376\ |deg| West * patch of level sea ice in the midst of otherwise mostly deformed (rubble) ice * ice thickness at deployment: 0.85 m. Snow depth: 0.04 to 0.05 m * air temperature on day of deployment: -41 |deg| C * no sediment visible in ice cores, but measurable after filtering Installed by: Chris Petrich, Andy Mahoney, Marcel Nicolaus Project: SIZONet Phase II, NSF grant number 0856967 Features ======== The design of this mass balance probe underwent a small change since the season 2010/11: the air temperature sensor moved to the antenna mast, and the under-ice sounder is supported differently to minimize vertical slip in spring. The probe comprises of a thermistor string, acoustic rangers for snow depth, ice thickness, and sealevel changes, air temperature and humidity sensor, and a wind turbine. All sensors and equipment operate over a wide voltage range, down to 9 V or below. They are powered by a wind turbine and lead-acid batteries that provide power at a voltage between 10.5 V and 15 V. In 2011, a suite of radiometers was deployed 15 m West of the Mass Balance probe with snow depth sounders operated by this mass balance probe. Remote Site ----------- * Location: on Chukchi Sea ice, South of Point Barrow * Cables: protected from fox bites with Aluminum Flexible Conduit * Data logger: Campbell Scientific - CR10X Data Logger (new backup battery this season) - AM1664 Multiplexer - SM5M Data storage module - SC32A Adaptor * Data link: - FreeWave FGR 115-WC radio (slave mode) + bridging RS232 connection + 900 MHz, spread-spectrum, no-licence - Bluewave 10 dB directional Yagi Antenna (BMY89K) * Batteries: 2\ |times| Exide 85 Ah in parallel * Thermistor string (CRREL-type, built in fall 2009) - white PVC rod, white potting, cold flex cable - 2 sections of 15 thermistors each, type YSI 44033 (approx. 10k\ |Ohm| at -6 |degC|) - 10 cm vertical separation - upper-most thermistor is 70 cm above |ice-snow| interface - thermistors are partially exposed at the North-side of the string * Under-ice measurements, attached to a dedicated mast penetrating sea ice - Ice thickness sounder: upward-looking acoustic altimeter Benthos PSA-916 - Sealevel sounder: downward-looking acoustic altimeter Benthos PSA-916 - Seawater temperature: thermistor, Campbell Scientific 107 * 3 Snow depth sounders, downward-looking Campbell Scientific - SR50 (SID 2) above Benthos ice thickness sounder - SR50a (SID 1) above in/under-ice radiometers - SR50a (SID 0) at downward-looking radiometer * Air temperature and humidity: - Campbell Scientific CS500 with shielding (new realtive humidity sensor as of Jan 2010) - 2.4 m above ground * Wind turbine: - Aero4Gen, 12 V, 100 W max. - LVM4SB12-T temperature-compensated charge controller, connected to the batteries in parallel Base Station ------------ * Located at NARL, supported by OIT (UAF) * Data link: - Bluewave 10 dB omni-directional antenna - FreeWave FGR 115-RC radio (master mode) + bridging RS232 connection + 900 MHz, spread-spectrum, no-licence - NPort 5110A-T serial device server * Virtual Machine, located at the BARC, supported by OIT - running MS Windows 2003 Server - LoggerNet 3.5.1 for scheduled data retrieval from data logger (polling data logger every 5 minutes) - Python 2.5 scripts tranfering data for processing at the University of Alaska Fairbanks (UAF) (sending new data every minute, if available) Data Acquisition and Processing =============================== * File name of data logger program: ``BRW_MBS10_JAN05_900.CSI`` (same program as 2009/2010 season) * Data are acquired every 15 minutes as instantaneous measurements (initial measurement interval was 2 minutes). Thermistor string readings are averages of 20 measurements taken in quick succession. * Snow depths, ice thickness, and water depth are measured as distances from the acoustic transducers. The transducer has a measurement cone of |PM|\ 10\ |deg| and evaluates the time of the first return signal. This eliminates systematic errors if the transducer is not mounted exactly perpendicular to the measured surface. A correction for the temperature-dependence of the speed of sound in water and air is applied, based on the water temperature measured with the Campbell Scientific 107 and the CS500, respectively. An offset is applied to convert a distance measurement to depth or thickness. * The script on the data logger corrects the readings of the Benthos sounders based on the temperature readings of the 107-L. Since those temperature readings are faulty, this correction is reversed during the generation of the "Processed Data", assuming the water temperature is constant at -1.8 |degC|. * The lowest temperature reading returned by the CS500 is -39.66 |degC|. This reading is also reported for lower temperatures. * Thermistor string measurements are performed as voltage measurements across the thermistor in a bridge with 10 k\ |Ohm| reference resistor (tolerance |PM|\ 0.1%), excited with 2500 mV. The thermistor resistance is determined from the measured voltage (assuming the reference resistor and exitation voltage are exactly 10 k\ |Ohm| and 2500 mV, respectively) and converted to temperature with the Steinhart\ |dash|\ Hart equation using coefficients fitted to the manufacturer's specifications of typical thermistors. Specifically, 1/*T* = *A* + *B* ln(*R*) + *C* [ ln(*R*) ]\ |^3| with *A* = 1.46843e-03, *B* = 2.38214e-04, *C* = 1.01608e-07, *R* in |Ohm| and *T* in K. The temperature error of this equation is less than 10 mK between -50 and +10 |degC|. * Each thermistor string uses its own reference resistor. After measuring the 15 thermistors of any string, the voltage over a bridge with 10 k\ |Ohm| control resistor is measured. The control resistor is mounted on the multiplexer board, and this reading should not change with time. Deviations likely indicate problems with at least one of: internal data logger measurement circuit, reference resistor, or control resistor. * Data gaps are filled with *invalid values* in the processed data file. Calibration and Errors ====================== No calibration is performed on any measurement apart from the processing steps outlined above. .. Note:: Temperatures are not calibrated. In particular, the following errors are not accounted for: * The pinger mast started to slip vertically downward by 2 June, and possibly as early as 30 May. As a result, snow depth (SID 2), ice thickness and sea level data are incorrect since 2 June. Also, rates of change are incorrect. However, the total thickness, snow plus ice, is correct. * The fixture of both SR50A was destroyed on day 124 between 21:30Z and 21:45Z (i.e. in the late morning, local time) for unknown reasons. The SR50A with SID0 and SID1 were mounted in different positions on days 141 and 139, respectively. At the time, the snow depth was not measured and hence the calculated snow depth since day 139 is inaccurate (error probably of the order of 5 cm). Summary: calculated snow/surface ablation rates are correct but absolute surface level is wrong starting day 139. * The temperature sensor 107-L seems to be faulty. While the water temperature signal measured at the thermistor string is in the same range as previous years, the signal of the 107-L is significantly different from both previous years and this year's measurements at the thermistor string. Problems became apparent approximately 3 days after deployment. Advise: do not use 107-L data of 2011. * Water depth is referenced to the |ice-snow| interface at the time of deployment rather than to the surface water level. Corrections need to be applied for ice growth and changing snow load. * Temperature measurements are accurate to typically |PM|\ 0.2 |degC|. * Relative humidity is specified by the manufacturer to be accurate to 10%. * Readings of the ice thickness sounder fluctuate. This could be due to changing acoustic path lengths as a result of brine release. * All depths and thicknesses in the processed data file are referenced to the |ice-snow| interface at the time of deployment. Interpretation of these numbers may differ due to surface ablation in June, and possibly from mid May due to the potential for superimposed ice formation. * The data logger clock is expected to remain accurate to better than 5 minutes from January through June. * During site inspection on April 1, 2011, it became apparent that the CS500 temperature/humidity sensor broke free from the radiation shield at some time between deplyment and April 1st (February saw a couple of storms moving through). Temporary fix may break loose during the season, in which case the temperature reading might be affected by sensor heating from solar irradiation. The shield will have to be replaced next season. * During site inspection on April 1, 2011, a significant amount of icing was found at the dump resistor of the charge controller of the wind turbine. Presumably, this is a result of blowing snow and heavy energy dissipation during the storms in February of sustained 40 knot winds, reaching 50 knots in gusts. File Format =========== Processed Data -------------- :File Name: ``BRW_MBS_2011.txt`` :Format: ASCII, columns TAB-delimited, rows terminated by LF :Header: TAB-delimited column headers in first row; first character is hash sign (#) :Invalid Values: -9999 ====== ================================================================================ Col. ====== ================================================================================ 1 Fractional day of 2011, UTC (1.0 for midnight January 1st) 2 Year (always 2011) 3 Integer day of year, UTC (1 for January 1st) 4 Time of day (HHMM), UTC 5 Internal data logger temperature (|degC|) 6 Supply voltage (V) 7 Water temperature from 107 probe (|degC|) 8 Relative Humidity from CS500 (%) (typ. 60\ |dash|\ 80%) 9 Air temperature from CS500 (|degC|), always above -40\ |degC| 10 Snow depth (m) from SR50a, SID 0 (albedo radiometer) 11 Snow depth (m) from SR50a, SID 1 (underwater radiometer) 12 Snow depth (m) from SR50, SID 2 ("pinger mast") 13 Ice thickness (m) 14 Water depth plus freeboard (m) 15 Control voltage (mV), upper thermistor string (typ. 1250) 16 Control voltage (mV), lower thermistor string (typ. 1250) 17 Thermistor temperature (|degC|) 70 cm above |ice-snow| interface 18 Thermistor temperature (|degC|) 60 cm above |ice-snow| interface ... ... 23 Thermistor temperature (|degC|) 10 cm above |ice-snow| interface 24 Thermistor temperature (|degC|) at |ice-snow| interface (in ice) 25 Thermistor temperature (|degC|) 10 cm below |ice-snow| interface ... ... 46 Thermistor temperature (|degC|) 220 cm below |ice-snow| interface ====== ================================================================================ Raw Data -------- :File Name: ``BRW_MBS_2011_raw.txt`` :Format: ASCII, columns TAB-delimited, rows terminated by LF :Header: none :Invalid Values: * CS500: RH negative or Temperature below -40 |degC| * PSA-916: distances below 0.5 m or above 5 m * SR50(a): -99999 ====== ================================================================================ Col. ====== ================================================================================ 1 Record identifier (always 110) 2 Year (always 2011) 3 Day of year Alaska Standard Time (AKST), UTC-9 (1 for January 1st) 4 Time of day (HHMM, leading zeros are dropped) in Alaska Standard Time (AKST), UTC-9 5 Internal data logger temperature (|degC|) 6 Supply voltage (V) 7 Water temperature from 107 probe (|degC|) 8 Relative Humidity from CS500 (%) (typ. 60\ |dash|\ 80%) 9 Air temperature from CS500 (|degC|) 10 Distance (m) measured by SR50a (SID 0) 11 Distance (m) measured by SR50a (SID 1) 12 Distance (m) measured by SR50 (SID 2) 13 Distance (m) measured by upward-looking PSA-916 14 Distance (m) measured by downward-looking PSA-916 15 Thermistor string voltage bridge reading 70 cm above |ice-snow| interface (mV) 16 Thermistor string voltage bridge reading 60 cm above |ice-snow| interface (mV) ... ... 21 Thermistor string voltage bridge reading 10 cm above |ice-snow| interface (mV) 22 Thermistor string voltage bridge reading at |ice-snow| interface (in ice) (mV) 23 Thermistor string voltage bridge reading 10 cm below |ice-snow| interface (mV) 24 Thermistor string voltage bridge reading 20 cm below |ice-snow| interface (mV) ... ... 29 Thermistor string voltage bridge reading 70 cm below |ice-snow| interface (mV) 30 Voltage bridge reading over control resistor for upper thermistor string (mV), should be about 1250 31 Thermistor string voltage bridge reading 80 cm below |ice-snow| interface (mV) 32 Thermistor string voltage bridge reading 90 cm below |ice-snow| interface (mV) ... ... 45 Thermistor string voltage bridge reading 220 cm below |ice-snow| interface (mV) 46 Voltage bridge reading over control resistor for lower thermistor string (mV), should be about 1250 ====== ================================================================================