Physical limnology WETA151 L6b Instruments. 9/14/2015 WETS150 Timo Huttula 2...

Physical limnologyWETA151

L6b

Instruments

04/21/23WETS150 Timo Huttula

2

ConductivityTemperatureDepth-probe

12 16 20 24läm pötila [°C ]

16

12

8

4

0

syvy

ys [m

]

Profiili 25

Profiili 24

Profiili 26

Profiili EXT2

Profiili EXT3

24-7-2003 P ro fi i l it 25 , 24 , 26 , E X T 2, E X T 3

0 2 4 6 8 10abs 440nm [m -1 ]

16

12

8

4

0

syvy

ys [m

]

Profiili 25

Profiili 24

Profiili 26

Profiili EXT2

Profiili EXT3

24-7-2003 P ro fi i l it 25 , 24 , 26 , E X T 2, E X T 3

04/21/23 WETS150 Timo Huttula 3

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


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 10-15 cm, shape: ball or double cone


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 300-500 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


Drogue measurement, 2

• In simplest form: boat and manual GPS– in one vertical you can follow a large group of drogues– in horizontal direction 300-500 m spacing is practical– waves and darkness are problem– lights and radar reflectors


Datasheet drog1.xls

JY/BIO1

Measurement: Current with droques Site:

Date Buoy Depth Start Start Start Start Start Stop Stop Stop Stop Stop Distance Direction Velcocity

identificationm Lat Lon Lat Lon time Lat Lon Lat Lon time km deg cm/s

61 xx.xxx N 23 xx.xxx E61.xxxxx 25.xxxxx xx.xx 61 xx.xxx N23 xx.xxx E61.xxxxx 23.xxxxx

25.7.2001 Plus 0.25 29.10 44.489 61.48495 23.74148 13:02 29.197 44.224 61.4866 23.7371 15:04 #NAME? #NAME? #NAME?

25.7.2001 Minus 4.5 29.10 44.489 61.48495 23.74148 13:02 29.144 44.041 61.4857 23.734 15:04 #NAME? #NAME? #NAME?

Datasheet for drogue measurement


A drogue with GPS buoy

A result from lake Jyväsjärvi at 14.9.2002. 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.


+/- 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


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


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


Lake Karhijärvi 7.7. - 16.8.1993


+/- 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


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


+/- 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


Acoustic Doppler Current Profilers; History

• 1982, First model by RD Instruments, Self contained• 1983, Vessel mounted version• 1986, five 75-1200 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


ADCP is a radar, 1

• Four beams. Angle 200 • Measures the floating velocity of particles• Reflectors are mostly zooplankton


ADCP is a radar, 2

• Sends pulses (= pings) about 10-20 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


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


Acoustic Doppler current profiler, RDI Workhorse

IAA.pdf p. 18, p.69


Contaminated layer near boundaries in ADCP measurements

Also near transducer surface an off-set is left. It’s thickness is about one layer thickness


+/- 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


Turbidity meters

Transmissometer model BTG

Scattering meter model D&A OBS3+


Radiometers

•Likor 1800 UW spektro radiometer

• WetLab’s AC-9 absorption and scattering meter


Flow through instrument set up in

a boat

http://www.luode.net/

04/21/23 WETS150 Timo Huttula 2924.00 24.04 24.08 24.12

longitude [°E]

59.26

59.28

59.3

59.32

59.34

59.36

59.38

lati

tud

e [

°N]

0

4

8

12

16

20

m odelled spim [m g/l] 4th of October

24.00 24.04 24.08 24.12

longitude [°E]

59.26

59.28

59.3

59.32

59.34

59.36

59.38la

titu

de

[°N

]

0

4

8

12

16

20

watersam ple spim [m g/l] 4th of October

24.00 24.04 24.08 24.12

longitude [°E]

59.26

59.28

59.3

59.32

59.34

59.36

59.38la

titu

de

[°N

]

0

4

8

12

16

20

m odelled spim [m g/l] 26th of Novem ber

Turbidity of surface

waters during

dredging

This figure is based on standard water sampling and laboratory analyses

Figures based on flow through measurements


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

Physical limnology WETA151 L6b Instruments. 9/14/2015 WETS150 Timo Huttula 2...

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Transcript of Physical limnology WETA151 L6b Instruments. 9/14/2015 WETS150 Timo Huttula 2...