1 / 35

Passive Microwave Remote Sensing

Passive Microwave Remote Sensing. Lecture 11. Principals.

dannon
Download Presentation

Passive Microwave Remote Sensing

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Passive Microwave Remote Sensing Lecture 11

  2. Principals • While dominate wavelength of Earth is 9.7 um (thermal), a continuum of energy is emitted from Earth to the atmosphere. In fact, the Earth emits a steady stream of microwave energy as well, though it is relatively weak in intensity due to its long wavelength. • The spatial resolution usually low (kms) since the weak signal. • A suit of radiometers can record it. They measure the brightness temperature emitted from the terrain or the atmospheric gasses, dusts. This is much like the thermal infrared radiometer for temperature measurement as we discussed before. • A matrix of brightness temperature values can then be used to construct a passive microwave image. • To measure soil moisture, precipitation, ice water content, sea-surface temperature, snow-ice temperature, and etc., based on brightness temperature images.

  3. Rayleigh-Jeans approximation of Planck’s law Thermal infrared domain (Planck’s law): Microwave domain (Rayleigh-Jeans approximation): Recall Let We have We have Unit is Wm-2Hz

  4. Unit is W•m-2•Hz•sr • For a Lambertian surface, the surface brightness radiation B(v,T), • The really useful simplification involves emissivity and brightness temperature in microwave range: In comparison with thermal infrared: (TB)4 = ελ(T)4

  5. Some important passive microwave radiometers • Special Sensor Mirowave/Imager (SSM/I) • It was onboard the Defense Meterorological Satellite Program (DMSP) since 1987 • It measure the microwave brightness temperatures of atmosphere, ocean, and terrain at 19.35, 22.23, 37, and 85.5 GHz. • TRMM microwave imager (TMI) • It is based on SSM/I, and added one more frequency of 10.7 GHz.

  6. AMSR-E • Advanced Microwave Scanning Radiometer – EOS • It observes atmospheric, land, oceanic, and cryospheric parameters, including precipitation, sea surface temperatures, ice concentrations, snow water equivalent, surface wetness, wind speed, atmospheric cloud water, and water vapor. • At the AMSR-E low-frequency channels, the atmosphere is relatively transparent, and the polarization and spectral characteristics of the received microwave radiation are dominated by emission and scattering at the Earth surface. • Over land, the emission and scattering depend primarily on the water content of the soil, the surface roughness and topography, the surface temperature, and the vegetation cover. • The surface brightness T (TB ) tend to increase with frequency due to the absorptive effects of water in soil and vegetation that also increase with frequency. However, as the frequency increase, scattering effects from the surface and vegetation also increase, acting as a factor to reduce the TB

  7. AMSR-E Najoku et al. 2005

  8. Example1: Snow depth or snow water equivalent (SWE) • The microwave brightness temperature emitted from a snow cover is related to the snow mass which can be represented by the combined snow density and depth, or the SWE (a hydrological quantity that is obtained from the product of snow depth and density). ∆Tb = Tb19V-Tb37V

  9. Large grains tend to scatter microwave radiation more than smaller grains Volume fraction (%) = snow density/900 From fresh snow to packsnow, the snow density increase from <100 kg m-3 to between 200-400 kg m-3 Kelly et al. 2003

  10. Example 1 3. Study Area (1)

  11. Impact of snow density (4)-mean SD Snow density = 0.4 g/cm3 or 400 kg m-3 Multi-snow density Wang, Xie, and Liang 2006

  12. Results: AMSR-E vs ground- SD at individual stations (snow density = 0.4 g/cm3)

  13. Results: AMSR-E vs ground- SD at individual stations (snow density = 0.4 g/cm3)

  14. Results: Annual change of SWE in YWR

  15. Example 2 Antarctic sea ice

  16. Footprint size 58 km 37 km 21 km 11 km 5 km Level 2 data

  17. Footprint size 58 km 37 km 21 km 11 km 5 km AMSR Bootstrap/ Ice temperature

  18. Footprint size 58 km 37 km 21 km 11 km 5 km AMSR Bootstrap/ Ice temperature Bootstrap

  19. Footprint size 58 km 37 km 21 km 11 km 5 km AMSR Bootstrap/ Ice temperature Bootstrap NASA Team 2/ Snow depth

  20. AMSR-E derived sea ice concentrations

  21. Ice Concentration/area Based on SMMR-SSM/I (http://nsidc.org)

  22. Compare AMSR-E ice concentration and NIC ice edge Cicek et al. 2009

  23. Snow cover • Idea: • Radiation from the ground is scattered by the snow cover. • The more snow the more scattering. • Scattering efficiency is frequency dependent. • hs = c (T37GHz-T19GHz) • Difficulties: • Different terrain forms (e.g., tundra, mountains, plains); different ice properties (FY/MY icel, ridges) • Scattering varies with snow physical properties (e.g., grain size, density, wetness) (From C.L. Parkinson, Earth from above,1997)

  24. Monthly snow depth data are derived from satellite passive microwave data

  25. A: Weddell Sea 7/86 - 9/86 (Wadhams et al., 1986) B: East Antarctic 10/88 - 12/88 (Allison et al., 1993) C: Weddell Sea 9/89 - 10/89 (Eicken et al., 19994) D: East Antartic 11/91 (Worby and Massom, 1991) E: Weddell Sea 6/92 - 7/92 (Drinkwater and Haas, 1994) F: East Antarctic 10/92 - 11/92 (Worby and Massom, 1995) G: East Antarctic 3/93 - 5/93 (Worby and Massom, 1995) H: Bellingshausen 8/93 - 9/93 (Worby et al., 1996) I: Amundsen 9/94 - 10/94 (Sturm et al., 1998) J: East Antarctic 9/94 - 10/94 (Jeffries et al., 1995) K: Ross Sea 5/95 - 6/95 (Sturm et al.,1998) L: Ross Sea/Bellingshausen 8/95-9/95 (Sturm et al., 1998)

  26. Inter-annual variability of September snow depth (on a pixel-by-pixel basis)

  27. Example 3 Radio-frequency interference contaminate the 6.9 and 10.7 GHz channels • Radio-frequency interference (RFI) includes the cable television relay, auxiliary broadcasting, mobile. RFI is several orders of magnitude higher than natural thermal emissions and is often directional and can be either continuous or intermittent. • Radio-frequency interference (RFI) is an increasingly serious problem for passive and active microwave sensing of the Earth. • The 6.9 GHz contamination is mostly in USA, Japan, and the Middle East. • The 10.7 GHz contamination is mostly in England, Italy, and Japan • RFI contamination compromise the science objectives of sensors that use 6.9 and 10.7 GHz (corresponding to the C-band and X-band in active microwave sensing) over land.

  28. radio-frequency interference (RFI) index (RI)

  29. Li et al. 2004

  30. 6.9 GHz contamination Najoku et al. 2005

More Related