development of a laser-based water level sensor for … school of sustainable infrastructure and...

Engineering School of Sustainable Infrastructure and Environment

Development of a Laser-Based Water Level Sensor for Fine-Scale Ecohydrological MeasurementsJoshua Benjamin, Dr. David Kaplan

November 7th, 2017


http://water.usgs.gov/edu/graphics/evapotranspiration.gif

Evapotranspiration (ET) is a critical component of the global water balance

ET accounts for 70-95% of incoming precipitation in Florida1

ET is difficult to pinpoint due to a lack of accurate and affordable sensor technology

Different types of measurement techniques

http://water.usgs.gov/edu/graphics/wctranspirationwatertable.gif

Background


White Method6

Developed by Walter White in 1932

Sy = Specific Yield

∆𝑠 = is the daily change in storage

R = net inflow/outflow rate [L/T]

Major assumptions6:

Diurnal water table fluctuations are a product of plant water use

Groundwater consumption negligible b/w midnight and 5 AM

Constant inflow/outflow rate

Specific yield is constant over time

𝐸𝑇 = 𝑆𝑦 ×∆𝑠

𝑡+ 𝑅


Current Technology Onset HOBO U20L Water Level Data Logger

Accuracy = 0.4 cm

Precision/Resolution = 0.14 cm

Cost = $300.00

Subject to errors (>1cm) from2:

Moisture accumulation

Differential heating across the system

Errors based on3:

Installation location and media

Differences in atmospheric and water temperature

Variations in solar radiation

Long equilibrium times

𝑝 = 𝜌𝑔ℎ

http://www.onsetcomp.com/files/styles/image_widget_large/public/product-images/HOBO-Water-Level-

Logger-U20L-01-apart_1.jpg?itok=KNSuKT0i


New Technology

http://www.solinst.com/products/data/images/Levelogger-Edge-Barologger-Edge.jpg

Leica DISTO E7100i4

Accuracy = ±0.15 cm

Resolution = 0.01 cm

IP54 Certified

Costs $150.00

Measurement Principle:

The Phase-Shift Method

c = the speed of light [L/T]

f = the modulation frequency [1/T]

Δφ is the phase shift between the measurement signal and the reference signal [L]

𝐷 =𝑐

2𝑓∙∆𝜑

2𝜋


Phase-Shift vs Time-of-Flight Time of Flight Method

c = the speed of light [L/T]

T = time [L]

More for long range distance measurements

Light is fast (300,000,000 m/s)

Phase-shift Method

f = the modulation frequency [1/T]

Δφ is the phase shift between the measurement signal and the reference signal [L]

Process signals w/ heterodyne method

mm-range resolution of 0.0015 to 60.96 m with non-cooperative targets

𝐷 =𝑐

2𝑓∙∆𝜑

2𝜋

https://upload.wikimedia.org/wikipedia/commons/4/40/Earth%27s_Moon_from_NOAA.jp

g

𝐷 =𝑐𝑡

2


The Phase-Shift Method

http://spot-on.net/images/Leica%20Disto-Measuring-Principles.pdf

𝐷 =𝑐

2𝑓∙∆𝜑

2𝜋


Sensor Components

http://lasers.leica-

geosystems.com/sites/default/files/product_images/e7100i

_left_top.jpg_c636653a1m.jpg

Leica DISTO E7100i5

Floating Target Platform

Next Thing Co. C.H.I.P.

http://images.bit-tech.net/content_images/2016/10/next-

thing-co-chip-and-pocketchip-review/chip-2b.jpg


Laser Mods Modified Laser to be USB

powered

Convert 5V to 3V – USB to AAA

Started out with a custom board


Laser Mod – Buck Converter

Modified Laser to be USB powered

Converts 5V to 3V – USB to AAA

Started out with a custom board, transitioned to a Buck converter mounted in a custom casing inside of the Disto battery casing


https://upload.wikimedia.org/wikipedia/commons/thumb/0/0a/Python.svg/2000px-Python.svg.pnghttps://upload.wikimedia.org/wikipedia/commons/thumb/9/9f/Bluetooth-Logo.svg/1280px-Bluetooth-Logo.svg.png

Written in Python

Interfaces between the computer and the laser

Has custom start and end time configurations

Exports data in a .txt format

https://eltechs.com/wp-content/uploads/2013/03/eltechs-sq-512-300x300.png

Laser.py


𝐹𝑏 = 𝛾𝑓𝑙𝑢𝑖𝑑∀𝑏𝑜𝑑𝑦Floating Target Platform


Floating Target Platform

𝐹𝑏 = 𝛾𝑓𝑙𝑢𝑖𝑑∀𝑏𝑜𝑑𝑦

Left is MK-IV

Right is MK-V


RSE Calculation 𝑅𝑆𝐸 = 𝑦2


Results – Early Lab Trial Residual Noise:

(Abs) (in mm)

TPT-BPT

Avg : 2.698 mm

LB-WLS

Avg: 0.083 mm

LB-WLS 32.5x LESS residual noise


Results – Later Lab Trial Residual Noise:

(Abs) (in mm)

TPT-BPT

Avg : 2.303 mm

LB-WLS

Avg: 0.163 mm

LB-WLS 14.1x LESS residual noise


Longleaf Flatwoods Preserve

Owned by the St. John’s Water Management District

2850 acres

Study site is Mesic Flatwoods w/ Pomona soil5 – sandy clay loam, established in 20036

http://www.worldatlas.com/img/locator/city/039/20039-gainesville-locator-map.jpg


Results – July Trial

Almost 60 cm difference Laser shifted in casing


Well Case Redesign


December Experimental Setup

1. Leica DISTO E7100i4

Located inside of front well cap

2. Floating Target Platform

Inside Back well

3. Next Thing Co. C.H.I.P.

Located inside of gray box

4. AGM Car Battery

Inside of Black Box

5. Onset HOBO Logger

Located Inside back well

1

3

2

4

5


Results – December Trial


December Trial Root Square Error

𝑅𝑆𝐸 = 𝑦2

LB-WLS Average = 0.05±0.04 cm/day

HOBO Logger Average = 0.19±0.16 cm/day


ET GraphLB-WLS Average = 0.19±0.06 cm/day


PET Average = 0.14±0.02 cm/day


ET 1:1 ComparisonLB-WLS Average = 0.19±0.06 cm/day


PET Average = 0.14±0.02 cm/day


ET:PET RatiosLB-WLS Average = 1.43±0.52

HOBO Logger Average = 1.80±0.82


Power Analysis

LB-WLS Component Power Consumption

DeviceMinimum

(Watt)

Maximum

(Watt)

Disto E7100i 0.10 0.35

Raspberry Pi 2B1.25 1.40

NTC CHIP 2.75 3.25

Note: Each device operates under 5V. Note that while

the CHIP uses more power than the Pi 2B, this is with an

attached touchscreen and keyboard, which allows for

easier data entry and retrieval in the field.

𝑡 = 𝐻𝐶

𝐼𝐻

𝑘 t is time [hr]

H is rated discharge time [hr]

C is capacity [Amp*hr]

I is the actual current [Amp]

k is the Peukert constant, which is 1.1 for an AGM battery.


Power Analysis 𝑡 = 𝐻𝐶

𝐼𝐻

𝑘

LB-WLS Component Power Consumption relative to the central buck converter

Parameter Maximum Load Minimum Load With LoPya

Current (out) [Amp] 0.72 0.620.17

Power (out) [W] 3.60 3.10 0.85

Current (in) [Amp] 0.40 0.340.09

Power (in) [W] 4.77 4.10 1.13

Est. Run Time [hr] 301 3551473

Est Run Time [days] 12.5 14.8 61.4

Note: These values assume that the efficiency (η) of the buck converter is 76%, Vout is 5V, Vin is 12V, and that Pin*η =

Pout, with P=VI, where P is power (W), V is Voltage (V), and I is current (Amp).

aLoPy measurements are potential values based on lab-scale readings and have not yet been experimentally verified.


Power Analysis𝐼𝐹 𝐸𝑛−1 − 𝐿 + 𝐶 ∗ 𝑆 > 𝐸𝑜

𝑇𝐻𝐸𝑁 𝐸𝑛 = 𝐸0𝐸𝐿𝑆𝐸 𝐸𝑛 = 𝐸𝑛−1 − 𝐿 + 𝐶 ∗ 𝑆

E0 = the Initial capacity of the battery (W*hr)

En-1 = the capacity in the previous step

En = the capacity in the calculated step

L = the load (W*hr)

C = a conditional statement, that is equal to 1 during peak sun and 0 when it is not peak sun

S = the solar cell energy generated per hour (W*hr).


Error Analysis

February Incorrect Installation

Dry well trial

May 2017

Periodic noise during the daytime


Error Analysis

Noise consistent across all dry trials

Possible Causes:

Temperature causes variation in air’s refractive index9

Optical Interference

Overall does not affect measurement accuracy

Important measurements during the night


Future Work Transition to a lower-power

computer

Reduce daytime measurement error

Connect to solar charging system for continuous usage

Implement remote access through LoRa


UF Watershed Ecology Group

People :

John Loeffler – 3D Printing

Jackson Benfer -Programming

Kevin Henson – Field Work

Acknowledgements


Thank you!Questions?


References1. McLaughlin, D., & Cohen, M. (2013). Realizing ecosystem services: wetland hydrologic function along a gradient of

ecosystem condition. Ecological Applications, 23(7), 1619–1631. doi:10.1890/12-1489.1

2. McLaughlin, D., and Cohen, M. (2011). “Thermal artifacts in measurements of fine‐scale water level variation.” Water Resources Research, 47(9), n/a–n/a.

3. Cain III, S. F., Davis, G. A., Loheide II, S. P., and Butler Jr., J. R. (2004). “Noise in Pressure Transducer Readings Produced by Variations in Solar Radiation.” Groundwater, Groundwater, 42(6), 939–944.

4. Leica Geosystems. (2016). “Leica DISTO E7100i.”

5. SJWMD, 2009. Longleaf Flatwoods Reserve Land Management Plan. St Johns Water Management District.

6. White, WN, 1932. A Method of Estimating Ground-Water Supplies Based on Discharge by Plants and Evaporation from Soil: Results of Investigations in Escalante Valley, Utah.

7. Loheide, S., J. Butler, and S. Gorelick, 2005. Estimation of Groundwater Consumption by Phreatophytes Using Diurnal Water Table Fluctuations: A Saturated‐unsaturated Flow Assessment. Water Resources Research 41:n/a–n/a.

8. McLaughlin, D., D. Kaplan, and M. Cohen, 2013. Managing Forests for Increased Regional Water Yield in the Southeastern U.S. Coastal Plain. JAWRA Journal of the American Water Resources Association

9. Shim, Y., O.-J. Kwon, H.-Y. Choi, and Y.-G. Han, 2015. Influence of Diverse Atmospheric Conditions on Optical Properties of a Pulse Laser in a Time-of-Flight Laser Range Finder. Journal of the Optical Society of Korea 19:1–6.


Current Technology

http://www.solinst.com/products/data/images/Levelogger-Edge-Barologger-Edge.jpg

Solinst Levelogger®-Barologger® Combo

Subject to errors (>1cm) from2:

Moisture accumulation

Differential heating across the system

Errors based on3:

Installation location and media

Differences in atmospheric and water temperature

Variations in solar radiation

Long equilibration times

𝑝 = 𝜌𝑔ℎ

Levelogger®

Accuracy = 0.3 cm

Precision/Resolution = 0.05 cm

Barologger ®

Accuracy = 0.1 cm

Resolution = 0.03 cm


SPECIFIC YIELD7𝑆𝑦𝑑−𝑐𝑜𝑚𝑝

𝑑 = 𝜃𝑠 − 𝜃𝑅 +𝜃𝑠 − 𝜃𝑅

1 + 𝛼 𝑑 𝑛 𝑚

Sy = specific yield

θs = the water content at saturation

θR = the residual water content

d = the depth to the water table [L]

α = van Genuchten coefficient [1/L].

N = van Genuchten coefficient

m = van Genuchten coefficient


Specific yield effect


Residual Noise (in mm)

Laser Based Water Level SensorTotal Pressure Transducer-Barometric Pressure

Transducer

Trial #Minimum

(abs)

Maximum

(abs)Mean (abs)

Minimum

(abs)

Maximum

(abs)Mean (abs)

1 0.002 0.279 0.099 0.085 9.153 2.865

2 0.001 0.234 0.067 0.070 6.287 2.532

3 0.005 0.666 0.163 0.184 7.519 2.303

Mean (#1-2)0.001 0.256 0.083 0.077 7.720 2.698

Mean (All) 0.003 0.393 0.110 0.113 7.653 2.566

Note. All values are absolute. Trial 3 data is treated separately due to the difference in experimental conditions.

Lab Trials Overall


Buffered TPT had lower overall temperature difference

Lab Trials Temperature Trends


December trial Residual Noise 𝑅𝑀𝑆 = 𝑦2

Residual Noise(cm)

Laser Based Water Level SensorTotal Pressure Transducer-Barometric Pressure

Transducer

Dates Minimum Maximum Mean Minimum Maximum Mean

12/7-12/13 0.0046 0.1205 0.0506 0.0204 0.5865 0.2272

12/15-

12/18 0.0023 0.1143 0.0405 0.0104 0.3751 0.1371

12/20-

12/24 0.0037 0.1022 0.0446 0.0155 0.5089 0.1887

12/26-

12/28 0.0005 0.1273 0.0581 0.0158 0.3883 0.1471

Mean 0.0028 0.1161 0.0484 0.0155 0.4647 0.1750

Mean w/

rain 0.0032 0.1127 0.0465 0.0161 0.5064 0.1886

Overall 0.0003 0.1949 0.0465 0.0009 0.9429 0.1886

Note. All values are absolute.

development of a laser-based water level sensor for … school of sustainable infrastructure and...

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