what happens to solar energy ? 1.absorption (absorptivity= ) results in conduction, convection and...
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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)