Transcript Surface albedo measurements

 Introduction
 Surface Albedo
 Albedo on different surfaces
 Seasonal change in albedo
 Aerosol radiative forcing
 Spectrometer (measure the surface albedo)
 Measurement of the albedo on gray concrete.
 Measurement of the albedo on black surfaces.
 Measurement of the albedo on grass surfaces
 Measurement of the albedo on water surface at different
zenith angles.
 Comparison of the surface albedo on different surfaces
 Conclusion
 Surface albedo is the fraction of
Sun’s radiation reflected from a
surface.
 Albedo is measured on a scale of 0
to 1
 value of zero indicates the surface
does not reflect, it absorbs all
valueincoming
of one means
that
light
. all incoming light is reflected
 value of one means that all
incoming light is reflected from the
surface.
 An ideal white body has an albedo
of 1 and an ideal black body has
albedo of 0
• Earth receives both short and long
wave radiation from the Sun
• Some radiation is reflected back to
space
– Albedo-global mean
planetary reflectance
• Clouds, air molecules,
particles, surface reflection
• Earth’s albedo  ~ 0.3
• About 30% of the incoming solar
flux is reflected back to space
• reflection of solar radiation are
due to ice, snow, clouds, aerosols,
and deserts surfaces.
 This graph shows the
land surface albedo
over wavelengths 4001000nm.
 From this graph we
can see that the
average albedo is
approximately 0.3 or
30% and peaks
around 900nm.
Liou Xie et .al. 2002
 This graph shows the curve of
reflection for red ceramics.
 Values of reflectance were
found to be around 9% in the
UV range.
 33% in the visible range
 79% in the infrared(IV) range
 The average albedo over all
wavelengths between 290.0
and 2500.0nm was found to be
67.7%
R. T. A. Prado, F. L. Ferreira/ Energy and Buildings 37 (2005) 295-300.
Williams et al., 1993.
AEROSOL RADIATIVE FORCING
Top of Atmosphere Idea
S 2
F  T (1  N ) [(1  a ) 2 (1  g ) 4a(1   )]
4
Single scattering approximation
S = Solar constant (1386 [W/m2])
T = Atmospheric transmission (0.8)
N = Cloudiness (0.5)
g = Asymmetry parameter (0.7)
w = Single scattering albedo (0.75)
a = Surface albedo (MODIS)
 = Aerosol optical depth
Chylek and Wong, GRL, 1995
Strong Impacts on Boundary
Layer Meteorology and Surface
Radiative Forcing.
Modified from Dr. Seth Olsen’s AGU Presentation 2006.
AEROSOL RADIATIVE FORCING
James Hansen, NASA
Climatologist
Red Tide spectrometer
 Low cost
 Small foot print (89.1mm x
63.3 mm)
 The spectral response from
350nm to 1000nm wavelength
 Utilizes a detector with 650
active pixel, that is 650 data
point in one full spectrum.
 Integration times as fast as 3
milliseconds
Spectrometer help to measure :
 Absorbance
 Transmission
 Reflectance
Solar Radiation
 Visible light (42% of solar energy)
 Near-infrared light (52%)
 Ultraviolet light (5%)
Albedo is the amount of sunlight
that is reflected by a particular
surface.
Black Asphalt
Date: 28th April, 2012
Time: 12:08 pm
Black Paper
Date: 1st May, 2012
Time: 4:35 pm
Zenith Angle = 27.0551°
Time: 12:08:03
Date: 4/28/2012
Albedo = 0.08 – 0.22
Zenith Angle = 27.0551°
Time: 12:08:03
Date: 4/28/2012
Albedo = 0.08 – 0.22
Zenith Angle = 64.5544°
Time: 16:35:00
Date: 05/01/2012
Albedo = 0.015 – 0.08
Zenith Angle = 64.5544°
Time: 16:35:00
Date: 05/01/2012
Albedo = 0.015 – 0.08
Date : 28th April, 2012
Time : 3:52 pm
Zenith Angle = 45.8890°
Time: 15:52:15
Date: 4/28/2012
Albedo = 0.22 – 0.42
(nm)
(nm)
Date: 28th April, 2012
Time: 11:50 am
Date: 28th April, 2012
Time: 12:00 pm
Green Grass
Zenith Angle = 28.8215°
Time: 11:50:02
Date: 4/28/2012
Albedo = 0.14 – 0.34
Dry grass
Zenith Angle =28.001°
Time: 12:00:30
Date: 4/28/2012
Albedo = 0.18 – 0.47
Green Grass
Zenith Angle = 28.8215°
Time: 11:50:02
Date: 4/28/2012
Albedo = 0.14 – 0.34
Dry grass
Zenith Angle = 28.001°
Time: 12:00:30
Date: 4/28/2012
Albedo = 0.18 – 0.47
Date: 29th April, 2012
Time: 1:19 pm
and
Time : 5:10 pm
Zenith Angle = 31.0610°
Time: 13:19:03
Date: 4/29/2012
Albedo = 0.1 – 0.27
Zenith Angle = 60.3233°
Time: 17:10:20
Date: 4/29/2012
Albedo = 0.31 – 0.76
Zenith Angle = 60.3233°
Time: 17:10:20
Date: 4/29/2012
Albedo = 0.31 – 0.76
Zenith Angle = 31.0610°
Time: 13:19:03
Date: 4/29/2012
Albedo = 0.1 – 0.27
Gray Concrete
Albedo
Albedo
Grass Surface
Water Surface
Black Road
Wavelength(nm)
Wavelength(nm)
Liou Xie et .al. 2002
Date: 12th April, 2012
Time: 4:30 pm
Date: 5th April, 2012
Time: 5:06 pm
Clear day
Zenith Angle = 67.5875°
Time: 16:30:30
Date: 4/12/2012
Albedo = 0.16 – 0.30
Clear day
Zenith Angle = 67.5875°
Time: 16:30:30
Date: 4/12/2012
Albedo = 0.16 – 0.30
(nm)
Cloudy day
Zenith Angle = 75.3181°
Time: 17:06:10
Date: 4/05/2012
Albedo = 0.01 – 0.22
(nm)
Cloudy day
Zenith Angle = 75.3181°
Time: 17:06:10
Date: 4/05/2012
Albedo = 0.01 – 0.22
(nm)
 Measuring and monitoring surface albedo plays an important role in the
earths energy balance and climate.
 The Surfaces which have albedo 1 or close to 1, reflect almost all incoming
solar radiation.
 Most surfaces that have an albedo of 1 or near 1 are white in color.
 The surfaces which have albedo zero or close to zero, absorb almost all
incoming radiation.
 Our measurements reveal that the albedo of black or dark surfaces was
very low, ranging from around zero to approximately 0.2.
 The albedo of grass varied from around 0.15 to 0.45 depending on the
condition of the grass.
 The albedo of water is dependent on the zenith angle and ranged from 0.1
to 0.76.
 Concrete was found to have the highest average albedo out of the surfaces
we measured, remaining at a fairly constant value of 0.3.
 Our measurements are consistent with current known surface albedo values
for various surfaces.