Lesson 1b – Stationary Sensors

(part 1) • General Concepts

– Physical, chemical,

biological transducers

– Time series sampling

• Sensor types

– Meteorology

– Terrestrial

– Aquatic

– Data transmission

• Applications

– Precision agriculture

– Water supply/flood

control

– Water quality monitoring

Motivation: Where do we use stationary sensors?

Drawing by Jason Fisher

UC Merced/WN/CENS-UCLA

A simple application

• Monitor flow and water quality flowing from a pipe to a

river (including interactions with groundwater)

• Perhaps this pipe is flowing from a town, or a factory,

or a farm…

• It would be costly to send people to sample every day

and night

Stationary Sensors Status and Outlook

Physical Sensors…increasingly smaller, cheaper

Chemical Sensors: gross concentrations, changes

Acoustic and Image data samples

Acoustic, Image sensors with on board analysis

Chemical Sensors: trace concentrations, universal sensors

(lab-on-a-chip)

DNA microarrays onboard embedded device, universal sensors

Sensor triggered sample collection (bridging technology)

present future

Organism tagging, tracking

ab

ioti

c

bio

tic

DNA biosensors for targeted microorganism

Physical Sensors

Parameter

Field-

Readiness Scalability Cost

Temperature High High 50–100

Moisture Content High High 100–500

Flow rate, Flow velocity High Medium–High 1,000–10,000

Pressure High High 500–1,000

Light Transmission (Turbidity) High High 800–2,000

Goldman et al. (2007)

[see course website]

Stationary Sensors for Monitoring:

Physical Properties

1. Meteorology (weather): Most common – Air temperature

– Humidity

– Wind speed, direction

– Precipitation

– Solar radiation

– Atmospheric pressure

• These systems are relatively robust because there is a large market for them – Range of prices (depends on

precision needed)

– Weather forecasting is obviously critical all over the world

– Many properties also important to industry (e.g., humidity)

Meteorology Sensors: Examples

• Air temperature – Many types (thermistors,

thermocouples, RTD, etc.)

• Important: Must have a radiation shield (preferably

equipped with a fan) to report true air temperature

Resistance temp detector (RTD)

Must be packaged

inside a radiation

shield like this

Meteorology Sensors: Examples

• Humidity – Typically analog or digital, based on

capacitance of a porous media that adsorbs moisture as

a function of humidity

• Typically packaged with air temperature sensor

Digital sensor +

display Basic analog sensor

(requires A/D board)

Meteorology Sensors: Examples

• Wind speed – Two main types (mechanical

anemometers, sonic anemometers)

• Important: Different applications require either simple

wind direction, or the wind vector (2D or 3D)

Self-orienting (1D)

windmill-type

anemometer

Self-orienting (1D) cup-

type anemometer

Sonic anemometers

(sound/Doppler

principle)

3D

2D

Meteorology Sensors: Examples • Solar Radiation – There is a spectrum of radiation (different

applications call for different measurements)

• Different mechanisms: photoelectric detectors (low-cost,

less precise); thermopile detectors (higher cost, more

precise)

• Applications: Meteorology, Solar energy potential,

Photosynthesis (ecology, agriculture)

Using different filters,

some radiometers are for

specific portions of the EM

spectrum (e.g., PAR =

photosynthetically active

radiation, 400-700 nm)

Meteorology Sensors: Examples • Solar Radiation – There is a spectrum of radiation

(different applications call for different measurements)

• Applications: Meteorology, Solar energy potential,

Photosynthesis (ecology, agriculture)

Radiometer typically has

a hemi-spherical ―dome‖

(left) or white radiation

collection area (right)

diffuse

diffuse

direct

Total or Global

Using different filters,

some radiometers are for

specific portions of the EM

spectrum (e.g., PAR =

photosynthetically active

radiation)

or

Meteorology Sensors: Examples • Atmospheric (barometric) pressure – Pressure

applications are plentiful, and pressure transducers are

cheap and small

Meteorology Sensors

• Rain gauge – Difficult, usually need to measure impulse

of rain impact, or weight of water to ―trip‖ a mechanism

―tipping bucket‖ digital rain gauge sensors Pressure plate (impulse)

rain gauge sensor

What are the advantages and disadvantages of each type?

Meteorology Sensors

• Sidenote: Vaisala

(Sweden) sells a weather

station with no moving

parts

• Variables:

– Preciptitation

– wind speed and direction (2D)

– barometric pressure

– Air temperature

• Does not provide solar

radiation

What do meteorology data look like? • Think about a weather station located at point A

• Look at 4 days worth of data

Point A

Sun’s daily trajectory

Day 1 Day 2 Day 3 Day 4 Day 5

Station 1

Precip (mm)

Station 2

Precip (mm)

2 weather stations 10 m apart Why are the responses different?

Class Problem 1: What do the data look like?

• Write down observations about the following meteorology data set

from ―Point A‖ on slide 15—in other words, explain the data

Day 1 Day 2 Day 3 Day 4 (note 00 = midnight)

Air Temp

(⁰C)

Bar. Pressure

(mm Hg)

Relative Humidity

(%)

Wind Speed

(m/s)

Solar Radiation

(W/m2)

inflow

Class Problem 2:

Recall the simple

watershed from lesson 1

Develop a list of sensors

needed to monitor this

watershed

In addition to placing the

sensors, what kind of

field work should you

need to do to help make

the sensor readings

meaningful?

Weather station; obs well; flow station