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Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Microwave Remote Sensing of Sea Ice
• What is Sea Ice ?
• Passive Microwave Remote Sensing of Sea Ice
• Basics
• Sea Ice Concentration
• Active Microwave Remote Sensing of Sea Ice
• Basics
• Sea Ice Type
• Sea Ice Motion
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Elachi, C., Introduction to the Physics and Techniques of Remote Sensing, Wiley Series in Remote Sensing, John Wiley & Sons, New York , 1987.
Basics - I
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Plancks‘ Law describes the spectral density of radiationemitted by a so-called blackbody with temperature T at frequency f. This law is valid for the entire frequencyrange.
Spectral radiation (Blackbody spectral brightness)Frequency(Surface) Temperature of the emitting bodySpeed of light (in vacuum)Plancks‘ constantBoltzmanns‘ constant
Basics – II: Planck 1
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
For low microwave frequencies Plancks‘ Law can besimplified (Rayleight-Jeans Law)
Taking into account:
„A blackbody is defined as an idealized, perfectlyopaque material that absorbs electromagnetic energy at all frequencies while reflecting none“
the physical temperature of a blackbody T equals itsbrightness temperature TB which in the microwavefrequency range is given by:
Basics – III: Planck 2
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Grey bodies reflect electromagnetic energy at certainfrequencies; accordingly absorption & emission can be
• Direction dependent
• Polarization dependent
Consequently, in the microwave frequency range, thebrightness temperature is smaller than the physicaltemperature & a function of the emissivity of theemitting body
Emissivity
Polarization
Sensor incidence angle
Basics – IV: Planck 3
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Via the relation: emissivity at frequency f the following relations can be obtained:
for the emissivities at horizontal ( h) and vertical ( v) polarization and at incidence angle Θ.
This applies for brightness temperatures, i.e. formeasurements of the thermal emission of electromagnetic radiation in the microwave (and also infrared) frequency range.
Basics – V: Emissivity 1
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Relation between reflection coefficients as a functionof incidence angle & frequency and the complexdielectric constant (assuming specular reflection …)
with:
Basics – VI: Emissivity 2
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Complex dielectric constant
Allows to quantify emissive capabilities of & penetrati ondepth of radiation into a material
Can be regarded as frequency-dependent measure forthe dielectric loss and/or the electric conductivity
Rule-of-thumb:
• Dry materials and/or materials with low salinity & high porosity have a low dielectric constant, i.e. ≤ 1 (dry snow, multiyear ice)
• Wet/humid materials and/or material with a high salinity have a high dielectric constant, i.e. > 5 (wetsnow, young sea ice)
Basics – VII: Emissivity 3
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Ulaby et al., Microwave Remote Sensing – Active and P assive, Vol III, Artech House Inc., 1986.
Basics – VIII
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Open water: few millimeters
Sea ice: very variable & frequency, incidence angle and ice type dependend
Firstyear ice, 5 GHz: 15 cm, 20 GHz: 3 cm
Multiyear ice, 5 GHz: 35 cm, 20 GHz: 9 cm
Much larger penetrationdepth for freshwater ice
Snow may influencepenetration depth
Ulaby et al., Microwave Remote Sensing – Active and P assive, Vol III, Artech House Inc., 1986.
Basics – IX: Penetration Depth 1
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Much smaller for wetthan for dry snowbecause of increa-sing electric loss:
5 GHz, 1%: 30 cm, 6%: 4 cm
18 GHz, 1%: 10 cm, 6%: <1cm
Ulaby et al., Microwave Remote Sensing – Active and P assive, Vol III, Artech House Inc., 1986.
Basics – X: Penetration Depth 2
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Ulaby et al., Microwave Remote Sensing – Active and P assive, Vol I, Addison-Wesley Publishing Company, London, 1981.
Is this all?
No!
Surface roughness & “internal” roughness cause scattering
Atmosphere causes attenuation, emission & scattering
Basics – XI: More? … Yes!
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Gloersen et al., Arctic and Antarctic sea ice, 1978-19 87. Satellite passive microwaveobservations and analysis, NASA SP-511, NASA, Washin gton, D.C., 1992.
Basics – XII: Atmosphere 1
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Ulaby et al., Microwave Remote Sensing – Active and P assive, Vol I, Addison-Wesley Publishing Company, London, 1981 (modi fied).
70K
21K
10K
19 GHz
37 GHz
85 GHz
Basics – XIII: Atmosphere 2
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Microwave brightnesstemperature change as a function of integrated watervapor content (x-axis) and cloud liquid water content (y-axis) as modeled for 85 GHz SSM/I
Top) calm water surface witha surface emissivity of 0.5
Bottom) wind-roughenedwater surface with a surfaceemissivity of 0.73; this isequivalent to about 50% icecover.
Kern, S., Ph.D. Thesis, 2001
Basics – XIV: Atmosphere 3
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Left) View of the Special Sensor Microwave / Imager(SSM/I), right) schematic view of its viewing geometry
Basics – XV: Sensors 1
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
• SSM/I
FOV [km]
Sampling [km]
Polarization
f [GHz]
13x1529x3740x5043x69
12.5252525
H,VH,VVH,V
85372219
Advanced Microwave Scanning Radiometer (AMSR-E)
43x75
10
H,V
7
29x51
10
H,V
11
FOV [km]
Sampling [km]
Polarization
f [GHz]
4x68x1418x3216x27
5101010
H,VH,VVH,V
89362419
Basics – XV: Sensors 2
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Methods & Parameters - I
Parameters to be derived:
Sea Ice Concentration (areal fraction covered by sea ice) + Area + Extent
Sea Ice Motion
Sea Ice Type
Snow depth on sea ice
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Methods & Parameters - II
Microwave Remote Sensing of Sea Ice, edited by F.D. Carsey, American Geophysical Union (AGU) Monograph 68, pp 2 9-46, AGU,
Washington D.C., 1992.
Open water: ���� High dielectric constants & high reflectivity ���� lowemissivity
Sea ice (FY): ���� Low dielectric constants & low reflectivity ���� high emissivity.
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Different Methods
• Visible:
• Infrared:
• Microwave:
vbright dark
reflected sun light
Surface Temperature
warm cold
„warm“ „cold“
Surface Temperature timesemissivity
Methods & Parameters - III
100% 0%
100% 0%
0% 100%
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Basics: T p(f) = C Tp,i(f) + (1 - C) Tp,w(f)
• C: Partial sea ice concentration
• Tp,i(f) & T p,w(f): Typical brightness temperatures (Tie points)
• Tp(f): Observed brightness temperature
Th(f)= 213 K C=?
Th,i(f)= 250 K
Th,w(f)= 150 K
Ice: C=1
Water: C=0
Fraction0,68
C=0.68 or
68%Fraction
0,32
from in-situ observations
from in-situ observations
Methods & Parameters - IV
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Algorithm 1 to calculate the total sea ice concentrationfrom SSM/I 19 & 37 GHz data:
• Basic equation:
CI: total ice concentration; TI & TO: tie points (as bright-ness temperature) of sea ice & open water; TB: actualbrightness temperature.
• Bootstrap Technique (see next slight)
• frequency mode : 19 & 37 GHz data, same polarization
• polarization mode : h & v polarization, one frequency
• Equation for Bootstrap algorithm: O
OII
Methods & Parameters – VI: Comiso 1
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
a) Scatterplot of brightness temperatures at 19 & 37GH z; b) Scheme of Bootstrap technique: line CD: open water, line BA: 100 % ice, T: actualbrightness temperature pair; Coefficients a, b, αααα, and ββββ: tie points.
Gloersen et al., Arctic and Antarctic sea ice, 1978-19 87. Satellite passive microwaveobservations and analysis, NASA SP-511, NASA, Washin gton, D.C., 1992. (modified)
0% ice
100% ice
80% ice
Methods & Parameters – VII: Comiso 2
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Methods & Parameters - V
Microwave Remote Sensing of Sea Ice, edited by F.D. Carsey, American Geophysical Union (AGU) Monograph 68, pp 2 9-46, AGU,
Washington D.C., 1992.
Open water: ���� High dielectric constants & high reflectivity ���� lowemissivity
Sea ice (FY): ���� Low dielectric constants & low reflectivity ���� high emissivity.
Large (small)polarization differencefor open water (seaice) at this incidenceangle (50°)
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Algorithm 2 to calculate the sea ice concentration (total and multiyear) from SSM/I 19 and 37 GHz data:
• Normalized brightness temperature polarizationdifference (also: polarization ratio) using 19 GHz data(carries main ice concentration information)
• Normalized brightness temperature frequencydifference (also: gradient ratio) using 37 & 19 GHz data(carries ice type information: old ice & firstyear ice)
Methods & Parameters – VIII: NASA-Team 1
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Fractions of first-year ice and multiyear ice can bewritten as linear combination of P and G as follows:
Coefficients F, D, & M from in-situ measurements of P & G over 100% open water, firstyear ice and multiyear ice(tie points).
Total ice concentration: Sum of these two fractions.
Developed for SMMR, modified for SSM/I & AMSR-E.
Southern Ocean: Ice types A & B rather than firstyear & multiyear ice.
Methods & Parameters – IX: NASA-Team 2
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Gloersen et al., Arctic and Antarctic sea ice, 1978-19 87. Satellite passive microwaveobservations and analysis, NASA SP-511, NASA, Washin gton, D.C., 1992. (modified)
Schematic view of NASA Team algorithm tie point triangle : open water (OW), first-year (FY) and multiyear ice (MY).
100% FY ice
100% MY ice
Weatherfilter
Methods & Parameters – X: NASA-Team 3
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Comiso and Steffen, Studies of Antarctic sea ice concent ration from satellite dataand their applications, J. Geophys. Res., 106(C12), 31,361-31,385, 2001.
Methods & Parameters – XI: Quality 1
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Comiso and Steffen, Studies of Antarctic sea ice concent ration from satellite dataand their applications, J. Geophys. Res., 106(C12), 31,361-31,385, 2001.
Methods & Parameters – XII: Quality 2
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Far left: Broadband albedo (Operational Linescan System ( OLS)); black boxes: location of boxes 1, 2, 3shown in middle & right.
Middle left: Sea ice concentration derived from the OLS imag e.
Right: SSM/I sea ice concentration using the NASA-Team (l eftimage) & the COMISO-Bootstrap algorithm (right image).
Comiso and Steffen, Studies of Antarctic sea ice concent ration from satellite dataand their applications, J. Geophys. Res., 106(C12), 31,361-31,385, 2001.
Methods & Parameters – XIII: Quality 3
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Above: Tiepoint trianglefor NASA-Team algorithm
Right: Impact of varyingice conditions (mixture of multi- and first-year ice) together with schematictiepoint triangle ( Fuhrhopet al., 1998, Fig. 4 )
Upper LayerSnowDensity:0.1 – 0.3 g/cm³
Upper LayerSnow GrainDiameter:0.55 – 1.05 mm
Lower LayerSnow GrainDiameter:1.3 – 1.8 mm
Methods & Parameters – XIV: Quality 4
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
Impact of varying atmo-spheric conditions forNASA-Team tiepointtriangle ( Oelke, IJRS, 1997 (top right); Fuhrhop et al., TGRS, 1998 (bottomright) ); L: clear sky but10m/s wind speed.
Values of GR > 0.05 aretypically flagged: C < 15%
Wind speed: 0 –25 m/s
Snowcloud: 0 –0.4 kg/m²
Water vapor + cloud:0.6-13 kg/m², 0-0.5 kg/m²
80%100%
50%20%
Methods & Parameters – XV: Quality 5
Microwave Remote Sensing of Sea Ice, October 25, 2010, San Antonio, Texas, USAStefan Kern, KlimaCampus / CliSAP, University of Hamburg, Hamburg, Germany
End of second part!