What happens to solar energy ?

1. Absorption (absorptivity=)

Results in conduction, convection

and long-wave emission

2. Transmission (transmissivity=)

3. Reflection (reflectivity=)

+ + = 1

Response varies with the surface type

Snow reflects 40 to 95% of solar energy and requires a phase change to increase above 0°C

Forests and oceans absorb more than dry lands Then why do dry lands still “heat up” more?

Oceans transmit solar energy and have a high heat capacity

Characteristics of Radiation

Energy due to rapid oscillations of electromagnetic fields, transferred by photons

The energy of a photon is equal to Planck’s constant, multiplied bythe speed of light, divided by thewavelength

All bodies above 0 K emit radiation

Black body emits maximum possible radiation per unit area.Emissivity, = 1.0

All bodies have an emissivity between 0 and 1

                                                      

E = hv

Electromagnetic Radiation

Consists of electrical field(E) and magnetic field (M)

Travels at speed of light (C)

The shorter the wavelength,the higher the frequency

This is important forunderstanding informationobtained in remote sensing

Stefan-Boltzmann Law

As the temperature of an object increases, more radiation is emitted each second

Temperature determines E, emitted

Higher frequencies (shorter wavelengths) are emitted from bodies at a higher temperature

Max Planck determined a characteristic emission curve whose shape is retained for radiation at 6000 K (Sun) and 300 K (Earth)

Energy emitted = (T0)4

Radiant flux or flux density refers to the rate of flowof radiation per unit area (eg., Wm-2)

Irradiance = incident radiant flux densityEmittance = emitted radiant flux density

Wien’s Displacement LawAs the temperature of a body increases, so does the total energy and the proportion of shorter wavelengths

max = (2.88 x 10-3)/(T0) *wavelength in metres

Sun’s max = 0.48 m Ultraviolet to infrared - 99% short-wave (0.15 to 3.0 m)

Earth’s max = 10 m Infrared - 99% longwave (3.0 to 100 m)

UV are shortestwavelengths practicalfor remote sensing

We are blind to everything except this narrow band

Microwaves are longestwavelengths used inremote sensing

Solarradiation

Terrestrialradiation

Transmission through the Atmosphere

Radiation emitted from Earth is of a much longer wavelength and is ofmuch lesser energy

Some wavelengths of E-M energy are absorbed and scatteredmore efficiently thanothers

H2O, CO2, and ozone have the strongest absorption spectra

TransmissionLight moves through asurface (eg. on a naturalsurface)Wavelength dependent(eg. leaves)

8-11 m window

                        

ALBEDO: April, 2002

White and red are high albedo,green and yellow are low albedo

Characteristic spectral responses of different surface types. Bands are thoseof the SPOT remote sensing satellite.

white snow 0.80-0.95old snow 0.40-0.60vegetation 0.15-0.30light colour soil 0.25-0.40dark colour soil 0.10clouds 0.50-0.90calm water 0.10 (noon)

March 3, 2009

DAYTIME:

Q* = K - K + L - LQ* = K* + L*

NIGHT:Q* = L*

K = solar (shortwave) radiation ↓ = incomingL = longwave (terrestrial radiation) ↑ = outgoingQ* = net all-wave radiation * = net

Radiation Balance

Radiation Balance Components

Source: NOAA

L

ConductionThe transfer of heat from molecule to molecule within a substance

Convection and Thermals

ConvectionThe transfer of heat by the mass movement of a substance (eg. air)

Rising air expands and cools

Sinking air is compressed and warms

The Hydrological Cycle

Heat capacityThe amount of heat energy absorbed (or released) by unit volume of a substance for a corresponding temperature rise (or fall) of 1 °C

Specific heatThe amount of heat energy absorbed (or released) by unit mass of a substance for a corresponding temperature rise (or fall) of 1 °C

Latent heatThe heat energy required to change a substance from one state to another

Sensible heatHeat energy that we can feel and sense with a thermometer

Thermometerand radiationshield

SENSIBLEHEAT

Radiation Sensors(PAR and K)

Raingauge

Datalogger

Photo: Weather station, Tausa,Cundinamarca, Colombia(3,243 m asl)

http://www.jgiesen.de/sunshine/index.htm

Check this out:

N

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

10 cm Air Temp (south-facing)10 cm Air Temp (north facing)

Dec 15, 2004Jan 19, 2005

Tem

pera

ture

(C)

-15

-10

-5

0

5

10

15

10 cm Soil Temp (south facing)

10 cm Soil Temp (north-facing)

Tem

pera

ture

(C)

Dec 15, 2004

Jan 19, 2005

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

10 cm Dewpoint (south facing)10 cm Dewpoint (north facing)

Dec 15, 2004 Jan 19, 2005

Tem

pera

ture

(C)

10 – 100 m●

0.0001 – 0.001 m●

Mie scattering0.01 to 1.0 m●

LONG PATH LENGTH OF LIGHT THROUGHTHE EARTH’S ATMOSPHERE

MOST OF THE THE VIOLET, BLUE AND GREEN LIGHT IS SCATTERED

(from Pacific)

(prairie cold)