temperature - Using Landsat 7 to go from NDVI to Emissivity -
i using landsat 7 calculate land surface derived temperature.
understand main concepts behind conversion, however, confused on how factor emissivity model.
using model builder calculations , have created several modules uses instruments gain, bias offset, landsat k1, , landsat k2 correction variables.
converted dn radiance values well.
now, need factor in last , confusing (for me) part: emissivity.
calculate emissivity using ndvi.
have model procedure built calculate ndvi layer (band4- band3)/(band4+ band3).
have calculated pv, fraction of vegetation calculated by: [ndvi - ndvi_min]/[ndvi_max-ndvi_min]^2.
now, using vegetation cover method, need ev , eg.
not understand how find these values calculate total emissivity value per cell.
does have idea on how can incorporate emissivity formulation?
confused on how derive value...
i believe emissivity included part of dataset. alternatively, emissivity databases exist (such aster database here: https://lpdaac.usgs.gov/about/news_archive/aster_global_emissivity_database_ged_product_release, , others maintained academic departments.)
values of ev = 0.99 , eg = 0.97 used, , method of selection discussed, on p. 436 here: ftp://atmosfera.cl/pub/elias/paula/2004_sobrino_rse.pdf (j.a. sobrino et al. land surface temperature retrieval landsat tm 5, remote sensing of environment 90, 2004, p. 434–440).
another approach taken here: http://fromgistors.blogspot.com/2014/01/estimation-of-land-surface-temperature.html
estimation of land surface temperature there several studies calculation of land surface temperature. instance, using ndvi estimation of land surface emissivity (sobrino, et al., 2004), or using land cover classification definition of land surface emissivity of each class (weng, et al. 2004).
for instance, emissivity (e) values of various land cover types provided in following table (from mallick, et al. 2012).
soil: 0.928 grass: 0.982 asphalt: 0.942 concrete: 0.937therefore, land surface temperature can calculated (weng, et al. 2004):
t = tb / [ 1 + (? * tb / ?) lne ]
where:
? = wavelength of emitted radiance
? = h * c / s (1.438 * 10^-2 m k)
h = planck’s constant (6.626 * 10^-34 js)
s = boltzmann constant (1.38 * 10^-23 j/k)
c = velocity of light (2.998 * 10^8 m/s)the values of ? thermal bands of landsat setellites listed in following table:
| satellite | band | center wavelength (µm) | | landsat 4, 5, , 7 | 6 | 11.45 | | landsat 8 | 10 | 10.8 | | landsat 8 | 11 | 12 |
further reading on emissivity selection, see section 2.3, emissivity retrieval, here: https://books.google.com/books?id=xn4uaylexnsc&lpg=pa51&ots=yqrmda2s1g&dq=vegetation%20and%20bare%20soil%20emissivity&pg=pa50#v=onepage&q&f=false