ICE, WIND,

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MICROWAVE RADIOMETRY
ICE, WIND, AND ASSORTED PARAMETERS
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Blackbody Radiation

• According to thermodynamic principles, all matter
  at temperatures greater than absolute zero both
  absorb and emit non-coherent EM energy (noise)
  simultaneously.
• The absorption of EM energy by a body causes its
  physical or thermodynamic temperature to rise
  which, in turn, results in an increase in the
  emitted EM radiation.
• When the body reaches its thermal equilibrium,
  its physical temperature is constant and the rate
  of energy absorbed is exactly matched by the rate
  of energy emitted.

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Microwave Radiometry

• In the microwave region of the EM spectrum,
  physical media radiate energy according to the
  Rayleigh-Jeans Law.
• Microwave Brightness Temperature, TB, of a medium
  is the product of the media emissivity and its
  physical temperature.

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• Radiative Transfer Theory states that the TB
  measured by a spaceborne radiometer is the linear
  sum of individual contributions from the
  atmosphere and surface.

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Microwave Emissivity

• Emissivity varies with
• EM wavelength (defines radiometer operating
  frequency)
• EM polarization incidence angle
• Geophysical parameters associated with the
  physical media.
• Atmospheric microwave emission is non-polarized
• Resonant absorption by water vapor (21 GHz, 183
  GHz, 325 GHz),
• Resonant absorption by oxygen (60 GHZ 120 GHz)
• Non-resonant absorption of hydrometeorological
  parameters (cloud water and rain).

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Microwave Emissivity cont-1

• Rain increases microwave brightness
• But rain can also reduce microwave emission by
  scattering
• When size of droplets become a significant
  fraction of the EM wavelength.
• Ocean microwave emission is strongly polarized
  and depends upon the dielectric properties of sea
  water.
• Emissivity is a function of salinity, sea surface
  temperature, and small scale ocean wave roughness
  (proportional to the surface frictional wind
  speed).

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Microwave Emissivity cont-2

• Sea ice microwave emission is weakly polarized
  and depends upon ice type and concentration.
• First year (FY) ice is saline and has a
  emissivity near unity ( gt 95 ).
• Multi-year, MY, sea ice has undergone a
  thaw/freeze cycle and has much less salt content.
  
• Emissivity of MY ice is less than FY ice
• Microwave brightness contrast is gt100 K between
  open water and FY and MY sea ice.

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Microwave Emissivity cont-3

• Microwave emission from snow-covered land depends
  upon snow depth
• Microwave emission from dry bare soil has nearly
  unity emissivity.
• TB decreases with increasing free water content
  (soil moisture).
• Vegetation cover also masks the surface
  emissivity for frequencies greater than 2 GHz
• It is not possible to discriminate between
  vegetation types.

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Microwave Remote Sensing

• Geophysical parameter retrieval involves
  inversion of multi-spectral brightness
  temperature measurements.
• Number of required independent radiometric
  observations is at least equal to the number of
  parameters.
• More independent measurements generally improve
  the accuracy of the retrieval.
• Brightness measurements at different EM
  wavelengths, polarizations, and incidence angles
  constitute independent radiometric measurements.

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183 GHz atmos. Water vapor

• 19.35 GHz, 37.0 GHz 85.5 GHz, V H-pol
• 22.235 GHz- V-pol only (atmospheric moisture obs.)

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• Defense Satellite Meteorological Program (DMSP)
• Special Sensor Microwave/Imager (SSM/I)

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• Defense Satellite Meteorological Program (DMSP)

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Overview

• SSM/I operational in July 1987 on the F-8
  satellite.
• Subsequent SSM/I's have flown on F- 10 (Nov.
  1990), F-11 (Dec. 1991), F-12 (Aug 1994), and
  F-13 (Mar. 1995)
• SSM/I is a seven channel passive microwave
  radiometer operating at four frequencies
• 19.35 GHz, 37.0 GHz 85.5 GHz, V H-pol
• 22.235 GHz- V-pol only
• Products include
• Atmos Precipitation, Total Precipitable Water,
  Cloud Liquid Water
• Ocean Surface Wind
• Land/Ice Snow Cover, Sea-Ice

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SSM/I - Brightness Temperature
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CLOUD LIQUID WATER

• Integrated cloud liquid water (CLW) is retrieved
  over ocean (due to the low emissivity
  background).
• CLW Algorithm uses measurements at 19, 37, and 85
  GHz. Use of the 85 GHz measurements allows for
  the retrieval of extremely low amounts of CLW.
• Two cloud products (ocean only)
• mean liquid water path (LWP)
• mean cloudiness fraction (CFR)

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PRECIPITATION

• SSM/I rainfall algorithm utilizes 85V GHz channel
  to detect the scattering of upwelling radiation
  by precipitation sized ice particles within the
  rain layer.
• Technique is applicable over land and ocean.
• Rain rate derived indirectly based on the
  relationship between the amount of ice in the
  rain layer to the actual rain fall on the
  surface.
• Additionally, over ocean, an emission rain
  algorithm, based upon the absorption of the
  upwelling radiation by rain and cloud water (at
  19 and 37 GHz) is blended with the scattering
  algorithm.

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PRECIPITATION
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Precipitation December 1998
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MICROWAVE WIND PRODUCTS PASSIVE
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Wind over the oceans

• Wind stress is important for forcing the ocean
• High quality, routine time series (high spatial
  and temporal resolution) needed for weather
  prediction models, ocean models

• Traditional method for ocean wind measurements
• ships
• buoys
• These are limited
• cover limited area

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Wind

• Scatterometers
• Sky Lab
• Seasat
• ERS-1, and ERS-2
• NSCAT
• SeaWinds
• Microwave
• SMMR
• SSM/I
• Geosat
• Analyses blend in situ, model, and sensor
  results

• Ocean response to winds waves
• capillary to swell
• This provides basis for wind remote sensing
• Sensors
• Radar (meas. Backscatter from capillary waves)
• Microwaves (depends on surface roughness)

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Wind microwave

• SMMR Scanning Multichannel Microwave Radiometer
• Flew on Nimbus-7
• Data at GSFC, JPL-PO DAAC
• 1979-1984

• SMMR 10 channels that are close to those of the
  SSM/I

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Wind microwave

• SSM/I (Special Sensor Microwave / Imager)
• Polar orbiter, near circular orbit,
  sun-synchronous, ca. 820 Km altitude
• Flies on Defense Meteorological Satellite
  Program (DMSP) (F-8, F-10, F-11, F-12, F-13
  satellites)
• Data to Air Force Global Weather Central, the
  Navy Fleet Numerical Oceanography Center (FNOC),
  NGDC

• SSM/I seven-channel, four frequency,
  linearly-polarized, passive microwave radiometric
  system
• microwave brightness temperatures at 19.35,
  22.235, 37.0 and 85.5 GHz

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Winds microwave

• Microwave data provide a measure of changes in
  the brightness temperature of the surface of the
  ocean, which may be related to the surface
  roughness

• Most current methods use statistical algorithms
  which mean or difference channel brightness
  temperatures Halpern et al., 1991. JPL
  Publication91-8, 110pp Wentz, F., et al., 1986
  JGR 91, C2, 2289 2307.

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Winds microwave

• Algorithm relates wind speed at 19.5 m above the
  surface to microwave emissivity estimated by
  brightness temperature obtained by two SSM/I
  channels (37 GHz VH), and radiative transfer
  models of atmospheric absorption

• Wind direction not derived from sensors. Rather,
  this is provided by ECMWF or other models or
  analyses.

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Winds microwave

• The effect of ocean wind speed is to "roughen"
  the calm surface through the formation of
  capillary waves and foam which increases the
  emissivity.
• The 37 GHz channels are the most sensitive to
  this phenomenon.
• Detection of wind speed variations are limited to
  mainly non- raining atmospheric conditions, as
  dense clouds and rain tend to mask the ocean
  surface.

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Winds microwave

• Atlas et al. 1993 in Atlas of satellite
  observations related to global change, p.
  129.
• Compared SSM/I wind products to buoys and ships
• Results
• Accuracy
• Speed2m/s and
• Direction22 degrees

• In Atlas et al., 93, average wind speed and
  streamline maps are shown. Average resultant
  speeds are underestimates because the maps were
  derived from separate averages of u and v
  components.
• In general, SSM/I winds agree well with ground
  truth, climatologies, and may be used for global
  studies, interannual variation studies, and
  updating models.

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OCEAN SURFACE WIND SPEED
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Ocean Surface Wind Speed - Dec. 1998
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MICROWAVE WIND PRODUCTS ACTIVE SCATTEROMETER
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Winds scatterometers

• Scatterometer high frequency radar that that
  transmits pulses of energy toward the ocean and
  measures the backscatter from the ocean surface.
• The scatterometer detects wind speed and
  direction over the Earths oceans by analyzing
  the backscatter from the small wind caused
  ripples (cats paws)

• History
• Skylab (1973-1974)
• Seasat (1978)
• ERS-1 and ERS-2
• NSCAT (1996-present)
• SeaWinds (1999)

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Stick Scatterometers
NSCAT on ADEOS-1 (NASA sensor on Japanese
satellite)
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Stick Scatterometers
Active Microwave Instrument (AMI) on ERS-1 and 2
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Scanning microwave scatterometer
QuikScat (NASA)
SeaWinds (NASA on ADEOS-2)
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BRAGG ELECTROMAGNETIC SCATTERING
Bragg scattering waves build up or destroy each
other
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NADIR BACKSCATTERING - PHYSICAL OPTICS
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CAPILLARY WAVE GROWTH WITH FRICTIION VELOCITY
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EFFECT OF ATMOSPHERIC STABILITY ON OCEAN WIND
PROFILE
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LOGARITHMIC RESPONSE OF NRCS TO OCEAN FRICTIONAL
VELOCITY
UPWIND OBSERVATION 30º INCIDENCE ANGLE
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NRCS SIGNATURE VS. WIND DIRECTION
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NRCS WIND DIRECTION SIGNATURE FOR VERTICAL AND
HORIZONTAL POLARIZATION
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KU - BAND (14 GHZ) NRCS WIND DIRECTIONAL
SIGNATURE VS. WIND SPEED
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Wind speed and direction validation of ERS-1 data
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NSCAT 1 day coverage
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Scalar wind from ERS (1 and 2) satellites and at
Margarita Island Airport
(Sample ERS weekly mean w, 1x1 degree
resolution)
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Wind microwave

• Www sites
• SSM/I
• http//podaac.jpl.nasa.gov2031/SENSOR_DOCS/ssmi.h
  tml
• http//www-nsidc.colorado.edu/NASA/GUIDE/EASE/
• http//www.ngdc.noaa.gov/dmsp/dmsp.html
• http//microwave.msfc.nasa.gov5721/sensor_documen
  ts/ssmi_sensor.html1.
• Http//podaac.jpl.nasa.gov2031/DATASET_DOCS/ssmi_
  wentz.html3.
• SSM/I and SMMR
• http//podaac.jpl.nasa.gov2031/SENSOR_DOCS/smmr.h
  tml
• http//podaac.jpl.nasa.gov/SSMR_Products.htmlProd
  uct30