A LowCost Bathymeter Using Commercial OffTheShelf Components

1
A Low-Cost Bathymeter Using Commercial
Off-The-Shelf Components

• R. Kremens, J. Faulring, N. Raqueno
• Rochester Institute of Technology Center for
  Imaging Science

2
A Low-Cost Bathymeter Using Commercial
Off-The-Shelf Components

• A Low-Cost Bathymeter Using Commercial
  Off-The-Shelf Components
• R. Kremens, J. Faulring, N. Raqueno
• Rochester Institute of Technology Center for
  Imaging Science
• A low cost bathymeter suitable for generation of
  bottom profile maps of small to mid-size lakes
  has been developed. The device uses readily
  available commercial components for depth finding
  (Garmin Fishfinder 100 depth sounder) and
  positioning (Garmin GPS eTrex) combined with a
  custom electronic circuit board that provides
  data storage and management. Several data
  acquisition modes (e.g. manual, timed or
  fixed-distance sampling) are available. Eight
  analog inputs are also available to measure
  output from temperature, turbidity, pH or other
  sensors. The unit is light, waterproof and
  self-contained and can be deployed from canoes or
  larger powered vessels. Data from the bathymeter
  can be automatically downloaded into popular
  spreadsheet or GIS applications. Measured bottom
  profile maps from Coneseus Lake, NY will be
  shown, along with estimates on performance
  accuracy obtained by comparison with manual
  soundings.

3
Depth profiles of small bodies of water are
difficult to obtain at low cost/effort

• Data for small bodies of water is either missing,
  old or simply anecdotal
• Hydrodynamic/pollution studies require knowledge
  of lake volume and bottom profiles
• Water levels may be affected by seasonal and
  periodic events (runoff and sedimentation) so
  frequent re-measurement may be required
• Even on large bodies of water (Great Lakes)
  near-shore data is often missing or inaccurate to
  shoaling, bottom movement, old data
• Design goal provide a low cost ( capable of semi-automatic depth profiling on
  small lakes ( to 100 m depth)

4
We have developed a position aware data
acquisition module (PADAM)

• The PADAM was developed to acquire data and
  provide alarms on the wildland fire line
• The PADAM is a versatile field data recorder
• 8 channel, 12 bit A/D
• Precision Thermistor conditioning unit
• /- 0.2 Co absolute temperature measurement
• Internal non-volatile memory (64kBytes)
• Radio or local (speaker) voice synthesis
• 1200 bps RTTY (transmit only) or Packet modem
  (2-way)
• GPS position detection
• Commercial radio transceiver fully integrated
• Battery life management
• Low power modes
• Power-down standby

5
Commercial SONAR hardware added to the PADAM
provides depth profiles

• We use an inexpensive Garmin Fishfinder 100 to
  measure depths by SONAR
• A Garmin GPS eTrex Legend with wide area
  augmentation system (WAAS) provides positional
  accuracy to about 3 meters
• Both commercial devices communicate with the
  PADAM via serial interface
• The depth finder and GPS use NMEA 0183 message
  protocol

6
A number of other environmental parameters may be
optionally recorded using this instrument

• Eight analog channels can record turbidity,
  downwelled radiance, weather parameters (relative
  humidity, wind direction, speed, barometric
  pressure)
• Enhanced data acquisition planned for this season
  
• We are developing a simple probe to measure
  pressure (depth) and temperature for
  determination of thermocline and other
  depth-temperature features
• Precision temperature measurement using YSI
  thermistor conditioning unit provides surface
  temperature (at depth transducer)

7
The instrument is self-contained, water tight and
can operate for 3 weeks of data days without
recharging

• Uses NEMA Type 4 waterproof fiberglass housing
• Total weight of under 6 pounds makes the unit
  suitable for kayaks, canoes or larger vessels
• Rechargeable gel-cell battery provides 50-70
  hours continuous data recording
• On-board memory module holds 1850 data points
• 19 hectares at 10 m spatial resolution
• Suitable for complete map of small pond
• Increased memory larger surveyed area

8
The bathymeter operates in both manual and
automatic modes

• The device has several data collection modes
• Manual Records GPS position and depth on
  command from user
• Timed automatic records GPS position and depth
  at a pre-determined time interval
• Data can be acquired at 1 s intervals (limited
  by GPS readout)
• Fixed distance automatic records position and
  depth after moving a specified UTM, latitude or
  longitude

9
On return to shore, the data is downloaded to a
PC using a simple application

• Applications developed in MS Visual Basic allow
  secure downloading with data set description
  information
• Direct import into MS Excel or ArcView GIS
  application
• Can optionally download data to PDA using custom
  application

10
Results Near-shore bottom profiling of Conesus
Lake, NY

• The unit was deployed from a canoe paddled around
  the shore
• Even though this is a relatively large lake,
  bottom profile is poorly known
• USDA runoff investigation requires accurate
  knowledge of volume, bottom profiles, etc. for
  hydrodynamic calculations

11
Results Near-shore bottom profiling of Conesus
Lake, NY (2)

• We obtained high-resolution profiles of a stream
  entrance into the lake
• The unit provided very good agreement with
  conventional (weight sounding) methods
• We believe this device is more accurate than hand
  sampling!

• By analyzing the strength of the SONAR return we
  can provide rudimentary and automatic
  determination of bottom type (soft, hard,
  planted)

12
The unit was able to provide useful depth
profiles in the study area in an hour using an
unpowered vessel

• Study area is a stream outflow into the lake
• Using random position, timed sampling acquired
  about 150 points in one hour with 0.1 m
  resolution
• Bottom map is far superior to what is available
  from conventional sources

13
We will incorporate a number of improvements this
season

• Larger memory (256Kbytes) to allow longer data
  collection without data downloading
• Surface water temperature and turbidity using
  thermistor and IR scattering cell
• Turbidity at depth using weighted probe (10m?)
• Vertical position sensor using two-axis silicon
  accelerometer to remove angle effects caused by
  wave action
• Ability to add comments to data recording using
  PDA
• All this adds complexity and cost is it worth
  it?