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 by
the speed of light, divided by the
wavelength
E = hv

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
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 for
understanding information
obtained 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 flow
of radiation per unit area (eg., Wm-2)
Irradiance
Emittance
=
=
incident radiant flux density
emitted radiant flux density
Wien’s Displacement Law
As 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)
Terrestrial
radiation
Microwaves are longest
wavelengths used in
remote sensing
Solar
radiation
We are blind to
everything except
this narrow band
UV are shortest
wavelengths practical
for remote sensing
Transmission through the Atmosphere
Some wavelengths of
E-M energy are
absorbed and scattered
more efficiently than
others
H2 O, CO 2, and ozone
have the strongest
absorption spectra
Transmission
Light moves through a
surface (eg. on a natural
8-11 m window
surface)
Wavelength dependent
(eg. leaves)
Radiation emitted from Earth is of
a much longer wavelength and is of
much lesser energy
ALBEDO: April, 2002
White and red
are high albedo,
green and yellow
are low albedo
Characteristic spectral responses of different surface types. Bands are those
of the SPOT remote sensing satellite.
white snow
0.80-0.95
old snow
0.40-0.60
vegetation
0.15-0.30
light colour soil
0.25-0.40
dark colour soil
0.10
clouds
0.50-0.90
calm water
0.10 (noon)
March 3, 2009
Radiation Balance
K = solar (shortwave) radiation
L = longwave (terrestrial radiation)
Q* = net all-wave radiation
↓ = incoming
↑ = outgoing
* = net
DAYTIME:
Q* = K - K + L - L
Q* = K* + L*
NIGHT:
Q* = L*
Radiation Balance Components
L
Source: NOAA
Conduction
The transfer of heat
from molecule to
molecule within a
substance
Convection and Thermals
Convection
The 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 capacity
The amount of heat energy absorbed
(or released) by unit volume of a substance
for a corresponding temperature rise
(or fall) of 1 °C
Specific heat
The amount of heat energy absorbed
(or released) by unit mass of a substance for a
corresponding temperature rise
(or fall) of 1 °C
Latent heat
The heat energy required
to change a substance
from one state to another
Sensible heat
Heat energy that we can feel
and sense with a thermometer
Radiation Sensors
(PAR and K)
Thermometer
and radiation
shield
SENSIBLE
HEAT
Photo:
Weather station, Tausa,
Cundinamarca, Colombia
(3,243 m asl)
Raingauge
Datalogger
Check this out:
http://www.jgiesen.de/sunshine/index.htm
N
Temperature (C)
20
15
10
5
0
-5
-10
-15
-20
-25
-30
-35
-40
Dec 15, 2004
Jan 19, 2005
10 cm Air Temp (south-facing)
10 cm Air Temp (north facing)
15
Dec 15, 2004
10
Temperature (C)
5
Jan 19, 2005
0
-5
-10
-15
10 cm Soil Temp (south facing)
10 cm Soil Temp (north-facing)
10
Dec 15, 2004
Jan 19, 2005
5
0
Temperature (C)
-5
-10
-15
-20
-25
-30
-35
-40
-45
10 cm Dewpoint (south facing)
10 cm Dewpoint (north facing)
●
10 – 100 m
●
0.0001 – 0.001 m
Mie scattering
● 0.01 to 1.0 m
LONG PATH LENGTH OF LIGHT THROUGH
THE EARTH’S ATMOSPHERE
MOST OF THE THE VIOLET, BLUE AND
GREEN LIGHT IS SCATTERED
(from Pacific)
(prairie cold)