laser-based water level sensing: seeing the unseen

Engineering School of Sustainable Infrastructure and Environment

Laser-based Water Level Sensing:Seeing the Unseen

Joshua Benjamin, Dr. David Kaplan

November 6th, 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

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

Background


White Method2,3

Developed by Walter White in 1932

Sy = Specific Yield

∆𝑠 = is the daily change in storage

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

Major assumptions2:

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) from4:

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 Leica DISTO E7100i5

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

http://lasers.leica-

geosystems.com/sites/default/files/product_images/e7100i_left_top.jpg_c636653a1m.jpg


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


𝐹𝑏 = 𝛾𝑓𝑙𝑢𝑖𝑑∀𝑏𝑜𝑑𝑦Floating Target

Platform


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


Well Case Design


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


Experimental

Setup1. 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


RSE Calculation 𝑅𝑆𝐸 = 𝑦2


Measurement Root

Square Error

𝑅𝑆𝐸 = 𝑦2

LB-WLS Average = 0.05±0.04 cm/day

HOBO Logger Average = 0.19±0.16

cm/day


UF Watershed

Ecology Group

People :

John Loeffler – 3D

Printing

Jackson Benfer -

Programming

Kevin Henson –

Field Work

Acknowledgements


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. 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.

3. 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

4. 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.

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

6. SJWMD, 2009. Longleaf Flatwoods Reserve Land Management Plan. St Johns

Water Management District.