Team Philosoraptors:Temperature, Humidity, Pressure

Hannah GardinerJoe ValieantBill Freeman

Randy Dupuis

Goals and Objectives

• Goals

• Objectives

Science Objectives

• Layers of the atmosphere

• Time dependence

Technical Objectives

• Payload• Money and Weight• Measurements• Documentation

PDRPDR

CDRCDR

FRRFRR

Earth’s Atmosphere

Overview

• Troposphere– Clouds

• Stratosphere• Mesosphere• Thermosphere

Troposphere

• Atmospheric Conditions

• “Stirring”

Clouds

Stratosphere

• Atmospheric Conditions

• Ozone Layer

Mesosphere

• Atmospheric Conditions

• Measuring

Thermosphere

• Atmospheric conditions

• Start of “space”

Review

• Atmospheric layers

Weather Balloons

http://www.ehow.com/about_5050060_history-weather-balloons.html

Science Background

US Model Atmosphere 1976

• Produced by NOAA, NASA, and USAF– NOAA: National Oceanic and Atmospheric

Administration– NASA: National Aeronautics and Space

Administration– USAF: United States Air Force

US Model Atmosphere 1976

• Theoretical model of the atmosphere using:– Ideal gas law• p = DRT

– Hydrostatic Equilibrium law• dp/dh = -gD

p = Pressure of airD = Density of airR = Universal Gas ConstantT = Temperatureg = Acceleration due to gravity

US Model Atmosphere 1976

• Assumes:– Dry Air– Temperature is linear with altitude

• Can calculate properties of the atmosphere– Pressure– Temperature– Density– Speed of sound

Measured Temperature profile of the atmosphere

0 5 10 15 20 25 30 35-80

-60

-40

-20

0

20

40Temperature vs Altitude

Altitude [km]

Temperature[C]

Troposphere Tropopause Stratosphere

Measured Lapse Rate of the atmosphere

0 20000 40000 60000 80000 100000 1200000

1

2

3

4

5

6

7

8

9

10

Change in Temperature vs Altitude

Altitude [feet]

ΔTemp/alt[°C/km]

Troposphere Tropopause Stratosphere

Measured and theoretical pressure as a function of altitude

0 5 10 15 20 25 30 350.001

0.01

0.1

1

Pressure vs Altitude

MeasuredTheory

Altitude [km]

Pressure[atm]

Troposphere Tropopause Stratosphere

Measured humidity as a function of altitude

0 5 10 15 20 25 30 350

20

40

60

80

100

120

Humidity vs Altitude

Altitude [km]

Humidity[%rel]

Troposphere Tropopause Stratosphere

Measured humidity rate of change as a function of altitude

0 5 10 15 20 25 30 35-30

-20

-10

0

10

20

30

40

50

Humidity rate of change vs Altitude

Altitude [km]

ΔHum/alt[%rel/km]

Troposphere Tropopause Stratosphere

Temperature error and humidity as a function of altitude in the Troposphere

0 2 4 6 8 100

10

20

30

40

50

60

70

80

90

100

HumidityTdiff

Science Requirements

• Temperature

• Pressure

• Humidity

-70 °C

30 °C

10Pressure Sensor(atm)

0% 100%

Technical Requirements

• Payload must cost less than $500 and weigh less than 500 grams.

• Payload must have separate sensors to measure pressure, temperature, and humidity and a real time clock to timestamp data.

• Signal conditioning is required to transform the signal from the sensor to a signal that spans the range of the ADC on the BalloonSat.

• The payload must have enough memory available to take data every 10 seconds.

Sensor Information

• The payload must have temperature sensors that to measure temperatures between 30 and -70 °C on the inside and outside of the payload with a standard deviation of ± 1.7 °C

• The payload must have a pressure sensor to measure pressures between 1 and 0.008 atm with a standard deviation of ± 0.002 atm

• The payload must have a humidity sensor to measure humidity between 100 and 0 %rel with a standard deviation of ± 0.5 %rel

Temperature Sensors

• There are 2 different types contact and noncontact.• Contact Sensors function by producing an electrical

output based on the temperature of the sensor. These sensors are placed in contact with the target and if the sensor and target are in thermal equilibrium (no heat flow between the sensor and target) the target’s temperature can be measured

• Noncontact Sensors measure temperature using the thermal radiant power of the infrared or optical radiation from the targets surface.

• Some examples are Thermocouples, thermistor, RTD’s

Pressure Sensors

• Pressure sensors are mechanical elements that are designed to deflect when pressure is applied. The deflection can be measured and transduced to produce an electrical output.Examples include poteniometric, piezoressistive, capacitive, and piezoelectric sensors

Humidity Sensors

• There are three main types: capacitive, resistive, and thermal conductive.

• Capacitive sensors consist of a substrate with a thin film placed in between two conductive electrodes, as the relative humidity changes the capacitance changes.

• Resistive sensors measure the change in the impedance of a hygroscpoic medium.

• Thermal Conductive sensors measure the absolute humidity by using the difference of the thermal conductivity of dry air and air containing water vapor