Met. Instrum. Exam #1

What are the basic properties of meteorology?

Temperature, pressure, wind, humidity, precipitation, cloud coverage, visibility

What length and timescales does the field of meteorology encompass?

Centimeters to kilometers, seconds to decades

Why are units important for analyzing data?

Provides necessary context and makes the numbers accurate in terms of their units

What are the difference between a static and dynamic sensor response?

Static - measures inputs that are constant or change very slowly over time

Dynamic - measures inputs that change rapidly or varies over time

What are sensor errors?

the difference or deviation between a sensor’s reported measurement and the true value of the physical property it is measuring

Why is quality assurance important?

To ensure that weather data are accurate reliable, and credible for weather forecasting, climate research, etc.

What are two physical principle that temperature sensors use to measure temperature?

What error is critical to reduce with sensors measuring temperature?

Conduction errors (caused by heat transfer along the sensor body or wires rather than the medium itself)

What is one type of temperature sensor that works by thermal expansion?

Bimetallic strip sensor

What is one source of error for a mercury barometer?

Temperature variations

What is one advantage to using an aneroid barometer?

Contains no liquid, makes it safe, portable, less prone to spilling or breaking

What type of pressure sensor is used at ASOS station?

redundant digital capacitive barometer

What is the purpose of a proposal?

to persuade a decision-maker to approve, fund, or support a specific plan, project, or idea

What are the components of a proposal?

Title page, executive summary, problem statement, proposed solution, timeline and milestones, qualifications, conclusion and sign-off

Who are the main funding sources of meteorology and atmospheric science research?

NOAA, NSF, NASA, DOE, federal agencies

Hygrometry

Thermometry

Barometry

Radiometry

Anemometry

Atmometry

Hyetology

Photometry

Hygrometry - Measurement of humidity

Thermometry - Measurement of temperature

Barometry - measurement of pressure

Radiometry - study of radiation

Anemometry - measurement of wind speed

Atmometry - measurement of the rate at which water evaporates

Hydrology - study of precipitation

Photometry - study of measuring visible light

What are the scales of meteorology?

1) Microscale - millimeters to few km - less than a second to a few min

2) Mesoscale - few km - km - few minutes to hours

3) Synoptic Scale - 1,000-5,000 km - few days to week

4) Planetary/Global Scale - 2,500-25,000 km - weeks and beyond

Weather & Climate

Weather - what is happening in the atmosphere right now or over a few days

Climate - long-term pattern of weather in region over 30 years or more

Microscale

Turbulence cascade, turbulence production, thermals

Mesoscale

Tornadoes, Thunderstorms, local winds, MCSs and hurricanes

Synoptic Scale

fronts, cyclones, Rossby waves, monsoon

Global circulation

global circulation

Length

Mass

Time

Temperature

meters (m)

kilograms (kg)

time (s)

Kelvin (K)

Density

kgm^-3

Force

kgms^-2

Pressure

kgm^-1s^-2

Energy

kgm²s^-2

Power

kgm²s^-3

Who is Kelvin

• William Thomson (Lord Kelvin)

• apart of the project to install the first telegraph cable under the Atlantic Ocean

• Proposed an absolute temperature scale

• developed the second law of thermodynamics

Who is Pascal?

• invented a calculator called the masculine to help his father who was a tax collector

• invented the syringe and the hydraulic press

• Developed the field of probability

Sensor

• an element that receives energy from the measurand and produces an output signal related in some way to the measurand

Signal Conditioning Device

converts a signal from one form to another

Data Display

Display that shows data in either digital or analog

Analog vs. Digital Sensor

Analog - continuer signal representing physical measurements

Digital - discrete signals generated by digital modulation

What is an instrument?

Functional model of a simple measurement system

Measurand (variable to be measured) - sensor - ASC (signal proportional to the variable) - ADC - DSC - transmit - storage - display (delivery method)

Sensors:

• senses, measures, and detects the environment

• an element that receives energy from the measurand and produced an output signal related in some way to the measurand

• Output signals include mechanical deflection, changed in position, rotation rate resistance, voltage, and frequency

Energy is always…

taken from the measurand and noise is always added to the output signal

• no perfect measurement

Two types of Sensors:

In-situ & Remote

In-situ sensor

• measures the environment directly

• direct contact

• regular thermometer, rain gauge, liquid-in-glass thermometer, barometer

Remote Sensor

• measures the environment from a distance without direct contact

• Split into active & passive

Active:

• signal is sent out from radar instrument and the return of that signal is analyzed

Passive:

• Input signal provides the energy concerted to the output signal

• Satellite

Static Sensor Characteristics

• sensor characteristics that do not change after stabilization, they remain constant

• Input & output are not dependent on time

• the relationship between the input and output is constant

• these are characteristics that can be accounted for through calibration

Static Characteristics:

Repeatability, sensitivity, accuracy, resolution, threshold, linearity, hysteresis measurement range, drift

Static Characteristics: Repeatability

error caused by the inability of a sensor to represent the same value under identical conditions

Static Characteristics: Sensitivity

a measurement of the change in output of the sensor relative to a unit change in the input

Static Characteristics: Accuracy

lack of error

Static Characteristics: Resolution

the smallest increment of the measurand that can be sense digital vs. analog

Static Characteristics: Threshold

instruments with internal friction need an inout to increase from zero to some value in order to respond

Static Characteristics: Linearity

the transfer plot is a linear straight line within a specified range of the instrument

Static Characteristics: Hysteresis

an error, caused by sensor friction

Measurement Range

the allowed lower and upper limits of its input or output

Static Characteristics: Drift

an error cause by the physical changes in the instrument after calibration

Dynamics Sensor Characteristics:

• the time response of the instrument

• sensor receives energy from the measurand and then responds

Dynamic Characteristics:

Rise time, delay time, peak time, settling time, percent overshoot, steady state error

Dynamic Characteristics: Rise time

time it takes a sensor to pass between 10% to 90% of the steady state response

Dynamic Characteristics: Delay time

time it takes to reach 50% of the steady state value for the first time

Dynamic Characteristics: Peak time

time it takes to reach the maximum reading for the first time for a given excitement

Dynamic Characteristics: Settling time

time it takes the sensor to settle down to within a certain percentage of the steady state value

Dynamic Characteristics: Percent Overshoot

measure of the peak minus the steady state value

Dynamic Characteristics: Steady state error

the deviation of the actual steady-state value from the desired value, and it can be corrected b calibration

Primary vs. Secondary Input

• Primary - the desired input to a sensor, the measurand

• Secondary - undesirable, but unavoidable inputs to a sensor

ex - temperature sensitivity is a secondary input to an aneroid barometer

ex - radiation secondary input to a thermometer

• REDUCE secondary inputs as much as possible

ASC (Signal Conditioning Device)

• operations performed on a signal to convert it from one form to another, to increase amplitude, to reduce noise, or to compensate for undesirable side effects

Data Display

• transformed or amplified signal is displayed digitally or in analog form

• Analog - continuous signal representing physical measurements

• Digital - discrete signals generated by digital modulation

Accuracy & Precision

A- lack of error in a measurement

P- a measure of repeatability in values

• instruments report precision as imprecision

• lower value of imprecision means precision

Error:

actual measurements (true) minus the observed measurement (E= A - Om)

Why might an instrument not measure the true value of the variable of interest?

secondly input, etc

Types of Errors:

Static, dynamic, drift, exposure

Types of Errors: Static

• hysteresis, residual non-linearities, secondary input, random noise

reference value-observed value

Types of Errors: Dynamic

• error due to sensor responding

Types of Errors: Drift

neither static or dynamic, but a result of gaining equipment

satellite operate for decades

Types of Errors: Exposure

• error due to improper sensor exposure or failure to provide proper coupling between the sensor and the measurand

this type of error cannot be accounted for in the calibration process

(Greatest error)

Standards

• met measurements must abide by national and international standards

• important because affects day to day

• organizations that oversee standardizing meteorological measurements: NWS, National Institute of Standards and Technology, World Meteorological Organizations

Instruments MUST meet

Calibration standards, performance standards, exposure (proper placement), and procedural standards

System Integration

• data should be collected and transmitted in real time

• Power source, location, climate, resource all influence the implementation of a measurement systems

challenges of setting up instruments in extreme regions?

• insects, funding, accessibility, new to know deployment location

System Integration: Pt.2

• atmosphere covers surface to space

• Communication systems: Land-line, radio lines, satellites, wifi

• Power source

commercial power, battery power (thresholds of batteries), heaters

Quality Assurance

• Data w/o error is vital for numerous end user

Chapter 1: Review

• instruments are composed of sensors, signal conditioners, and data displays

• instrument sensors have static and dynamic characteristics

• instruments have numerous errors associated with them

• meteorological instruments must operate at industry standards

Thermometry

• the measurement of temperature

Why is measuring temperature important?

climate change, heat or extreme cold can be deadly, plant growth, economic fulxuations

Why are error in temp. measurement important to reduce?

seta a reaction off temp

Temperature sensors are divided into categories by the physical principle they use:

Thermal expansion, thermoelectric, electrical resistance, and electric capacitance

Thermal Expansion

• materials expand due to temperature

• expansion can be linear or non-linear

Bimetallic Strip

• pair of metals with different thermal expansion coefficients that are bonded together into a very thin strip

• at a reference temperature the strip maintains its shape

• as temperature changes the strip arcs ( distance the strip ares is related to temp)

Bimetallic Strip - Static Sensitivity

take the derivative of y with respect to change in temperature

Static Sensitivity def

a measure of the change in the output of the sensor relative to a unit change in the input

Liquid-in-glass thermometers

• glass tube with bulb at one end filled with a liquid and a scale fastened or etched on the glass tube

• Liquid is usually mercury or alcohol (both are good, depends on what you want)

Mercury (-38.8 degrees C, 356.7 degrees C) Alcohol (-114 degrees C, 78.3 degrees C)

• liquid and glass expands as temperature increases

Static sensitivity: take the derivative of height with respect to change in temperature

How do you increase the sensitivity of the liquid-in-glass thermometer?

increase the bulb volume and decrease the tube radius

Max thermometers are special LIGTs

• mounted horizontally, has a constriction in the capillary tube close to the bulb

• the mercury. when warmed passes the constriction

• when the mercury cools, the mercury in the bulb shrinks and the mercury above the constriction cannot pass bak into the bulb

• shake to reset the thermometer

Min thermometers are special LIGTs:

• mounted horizontally

• minimum thermometers has marker floating (dumbbell) in the capillary tube of alcohol

As temperatures decreases, the marker goes down the capillary tube with the alcohol due to surface tension

as the temperature increases, the marker remains in place and the alcohol flows around the marker

• the thermometer is reset by holding the thermometer upside down

Current (I):

the rate of flow of electric charge through a conductive material

units: Ampere (A)

Conductivity:

A measure of the ability of the material to conduct an electrical currents

units: Siemens/m (kg^-1m^-3s^-3A²)

Resistance:

measure of the opposition to current flow in an electrical circuit

units: (kgm²s^-3A^-2)

Voltage:

the difference in electrical potential between two points

units: V (kgm^-2s^-3A^-1)

Capacitance:

collect and store energy in the form of an electric charge

units: Farad (kg^-1m^-2s^4A²)

Thermocouple: Thermoelectric sensor

• a differential temperature sensor: measures the temperature difference between two junctions as a voltage is developed across the junctions

• wide temperature ranges, reliable, expensive, and may have fast responses

Electrical Resistance Sensor

• Temperature affects the conductivity and resistance of electrical conducts

resistance temperatures detectors (RTDs)

• conductivity of metals decreases with increasing temperature

• the resistance increased with increasing temperature

T^, conductivity d, omega ^

Semi-conductors: conductivity increases with increasing temperature, resistance decreases (called thermistors)

T^, resistance ^m omega d

Electric Resistance Sensors

• precision resistance thermometer

• our own weather tower

• -made of platinum

• stable, resists, corrosion, high melting point, high degree of purity

• expensive, sensitive to strain - cannot be bent

• linear, easy to calibrate

• wide temperature range

• has a sensitivity

Thermistors: Temperature-sensitive semiconductors

• metallic oxides

• large and non-linear temperature sensitivity

• rapid response to temperature changes

Properties of thermistors:

• drift with time

• can have slower response time if they are coated for protection

• hard to calibrate, highly non-linear

ASOS Temperature Sensors: Hygrothermometer

• resistive platinum wire temperature device to measure ambient temperature and a chilled mirror to determine dew point temperature

• six measurements a minute averaged for 1-minute average

Pyrometers determine…

the temperature of a medium through the amount of emitted thermal radiation

T^, omega ^, the other one d

Why could a temperature sensor’’s measurement of air temperature vary drastically from the actual air temperature?

heat Is flowing away or towards the sensor by conduction, convention, and radiation