Physical limnology WETA151 L6b Instruments

9/14/2015 WETS150 Timo Huttula 2 ConductivityTemperatureDepth-probe

9/14/2015WETS150 Timo Huttula3 Drogues; history Ancient: Anything floating with current has been used Operational network along Finnish coast from 1910 to 2nd World War on light house ships After the war around the world (wood pieces, apples, post cards, flow crosses and cylinders) Positioning from shore by eye, triangle measurement, radars Satellite buoys 15 years in seas Since 10 years GPS provided new possibilities

9/14/2015WETS150 Timo Huttula4 A droque at the depth of 5 m in Lake Issyk- Kul.IAA.pdf p-.109 A drogue consists of: –Cylinder : diameter of 60 cm, height 100 cm –Cross: A4 size (21*29 cm) –Rope: 2-3 mm –Buoy: Diameter about cm, shape: ball or double cone

9/14/2015WETS150 Timo Huttula5 Drogue measurement In simplest way: –You need droques, a boat and manual GPS –in one vertical you can follow a large group of drogues –in horizontal direction m spacing is practical –waves and darkness are problem –lights and radar reflectors Accuracy: GPS with 12 channels gives about 6 m  drifting distance of 60 m gives 10 % accuracy for droque measurement How long time for a measurement? –Let’s expect a water velocity of 5 cm/s –time=distance/velocity –For 60m travel you need time=(60 m)/(0.05 m/s)=1200 s = 10 min

9/14/2015WETS150 Timo Huttula6 Drogue measurement, 2 In simplest form: boat and manual GPS –in one vertical you can follow a large group of drogues –in horizontal direction m spacing is practical –waves and darkness are problem –lights and radar reflectors

9/14/2015WETS150 Timo Huttula7 Datasheet for drogue measurement

9/14/2015WETS150 Timo Huttula8 A drogue with GPS buoy A result from lake Jyväsjärvi at Wind was blowing weakly from north. Two drogues were placed at the depth of 0,7- 2,7 m. They were connected to the automatic GPS buoy.

9/14/2015WETS150 Timo Huttula9 +/- of drogues +++ very inexpensive, major cost is the cost of GPS (about 300 USD) +++ practical and easy to use ++ good learning and teaching tool -- laborious for long term measurements

9/14/2015WETS150 Timo Huttula10 Moored current meters For collecting time series of currents Velocity measured on basis of propeller or impeller revolutions Available for more than 30 years Recording capacity 2…12 months Moderate cost Buoy – rope- meter (1)-…meter (n)- anchor Deployment with surface buoy or subsurface buoy Representative sites: bathymetric survey, tentative model application, current mapping with ADCP Not on navigational routes Risk of loss

9/14/2015WETS150 Timo Huttula11 Statistical analysis of currents Cartesian components  direction information included Filtering  important time scales Auto correlation and spectral analysis  principal periods of oscillation Cross correlation  is there any correlation between currents at different sites?? Regression analysis  factors causing currents

9/14/2015WETS150 Timo Huttula12 Lake Karhijärvi

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9/14/2015WETS150 Timo Huttula14 +/- of Aanderaa and Endeco propeller RCM + inexpensive ++ durable and rugged +++ widely used -- not possible to measure near boundaries except Endeco near surface -need several instruments to cover the vertical and horizontal variation of currents

9/14/2015WETS150 Timo Huttula15 Ultrasonic current meter UCM50 Travelling time of acoustic pulses depends on the velocity of water Three pairs of sensors, with 3 MHz piezometric transducer/receivers In each pair the pulses are sent from both sides exactly at the same time The 3D current vector is obtained

9/14/2015WETS150 Timo Huttula16 +/- of UCM ++ Very accurate and sensitive meter +++ Can measure near boundaries + Basic measurements are easily done -- Not very dependable in operation - Needs calibration - Small producer

9/14/2015WETS150 Timo Huttula17 Acoustic Doppler Current Profilers; History 1982, First model by RD Instruments, Self contained 1983, Vessel mounted version 1986, five kHz, SC, VM and direct reading In Finland since 1987 R/V Aranda (VM) and 1989 R/V Muikku 1991, RDI BB-generation 1995, RDI, Workhorse 1997, SonnTek 1998, Norrtek

9/14/2015WETS150 Timo Huttula18 ADCP is a radar, 1 Four beams. Angle 20 0 Measures the floating velocity of particles Reflectors are mostly zooplankton

9/14/2015WETS150 Timo Huttula19 ADCP is a radar, 2 Sends pulses (= pings) about times in second Integrates over certain volume (eq. 1 m thickness), width of the samples is O(1 m) Movement of instrument platform has to extracted (bottom tracking or GPS can be used) Accuracy depends on integration time

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9/14/2015WETS150 Timo Huttula21 Sound velocity Absorption of energy is dependent on density Long waves decay less than short waves Water density is mainly dependent on temperature and salinity Reflections from density boundaries

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9/14/2015WETS150 Timo Huttula23 Acoustic Doppler current profiler, RDI Workhorse IAA.pdfIAA.pdf p. 18, p.69

9/14/2015WETS150 Timo Huttula24 Contaminated layer near boundaries in ADCP measurements Also near transducer surface an off-set is left. It’s thickness is about one layer thickness

9/14/2015WETS150 Timo Huttula25 +/- of ADCP +++ Collects lot of data + Fairly good software + Quite easy to use, --Tuning and data interpretation is demanding - Older ADCP’s: for seas ++New products ++Costs are coming down

9/14/2015WETS150 Timo Huttula26 Turbidity meters Transmissometer model BTG Scattering meter model D&A OBS3+

9/14/2015WETS150 Timo Huttula27 Radiometers Likor 1800 UW spektro radiometer WetLab’s AC-9 absorption and scattering meter

9/14/2015WETS150 Timo Huttula28 Flow through instrument set up in a boat

9/14/2015WETS150 Timo Huttula29 Turbidity of surface waters during dredging This figure is based on standard water sampling and laboratory analyses Figures based on flow through measurements

9/14/2015WETS150 Timo Huttula30 Reflection measurements Measurements –Above water surface  sensors are not affected by biofouling –Sensors are not so expensive as submerged or flow through meters –Accuracy is not very high –Large set of possible applications Monitoring diffuse loads Calibration of satellite images Monitoring dam infiltration