Updated Landsat 8 Reflectance Tutorial w/ Imagery
Surface Reflectance Methods & TOA. As of 4/24/16, there is UPDATED INFORMATION IN STEP 6 (as is explained in Step 6 below).
Landsat surface reflectance is available for free from the USGS but converting to surface reflectance independently can be useful if, for example, surface reflectance is not available for a particular scene (for whatever reason) or if reflectance is needed as soon as possible (or if you simply may prefer to convert the data yourself).
Data Download for Surface Reflectance (SR) Tutorial. Includes: 1) Landsat 8 DN imagery for tutorial, 2) corresponding USGS algorithm surface reflectance imagery for comparison (in native integer raster format; divide by 10,000 for surface reflectance units), and 3) a composite RGB surface reflectance image (based on tutorial values). See below for more information.
Tutorial Data Location (orange); Red Band Scatter (.032949)
July 30th, 2014; East Central Illinois, USA (orange extent; 23.7 km x 15.0 km)
Landsat surface reflectance is available for free from the USGS but converting to surface reflectance independently can be useful if, for example, surface reflectance is not available for a particular scene (for whatever reason) or if reflectance is needed as soon as possible. You need GIS software for the data. Free Quantum GIS (opens in a new tab to a page on this website to access and download Quantum GIS) can be used; or you can use other software, such as ArcGIS. See the Landsat 8 Surface Reflectance Comparison page for results information.
This tutorial is based on the original tutorial but has new imagery and a specific recommended method (GIS Ag Maps Preferred Method2 Surface Reflectance [PM2 SR]). Important to know: Image-based atmospheric correction for Landsat 8 imagery is much different than it is for other Landsat imagery.
The download above includes Landsat 8 digital number (DN) imagery for bands 2, 3, 4, 5, and 6 (blue, green, red, NIR, and SWIR, respectively), corresponding Landsat 8 USGS Surface Reflectance imagery for the same bands, and a composite bands image produced by PM2 SR imagery (click on the composite bands image with an Identify Tool and reflectance for the visible bands can be seen). The LandsatLook image is not included. The imagery is from the fourth area from the top on the Landat 8 Surface Reflectance Comparison page.
* GIS Ag Maps Preferred Method Surface Reflectance Steps (PM SR & PM2 SR) *
(See table below tutorial steps for converted surface reflectance values after completing tutorial)
The GIS Ag Maps Preferred Surface Reflectance Method is outlined in the steps below and uses DOS with relative scatter based on band 4 (red) for the visible bands and TOA reflectance for band 5 (NIR) and band 6 (SWIR) because it is closer to USGS Landsat 8 surface reflectance than values with minor relative scatter deducted (as is shown in the Landsat 8 Surface Reflectance Comparison page). The relative scatter table can be accessed here: Landsat 8 Continuous Relative Scatter Lookup Table (opens in new window).
Steps to calculate the Preferred Method surface Landsat 8 with the Continuous Relative Scatter Lookup Table are as follows:
1) Apply the following equation to the entire raster for each band: ([DN x .00002] - 0.1).
2) Divide the values from Step 1 by the cosine of the solar zenith to calculate Top of the Atmosphere (TOA) reflectance. The solar zenith = (90 - solar elevation); the scene center solar elevation is given in the .MTL file can be used (or a more local value can be used if available). The cosine of the solar zenith angle for the data in the tutorial is 0.878335597. TOA is not surface reflectance but should be used for surface reflectance for band 5 (NIR) and band 6 (SWIR) as is shown in the Comparison page at the top. (There is very little scatter in the NIR and SWIR bands; small amounts are listed for NIR in the Relative Scatter Lookup Table. Nevertheless, values are closer to USGS Landsat 8 surface reflectance when NIR scatter is not deducted.)
3) Establish the starting scatter value (dark object) using the band 4 (red) Lowest Valid Value (also described in Dark Object Method link near top of page) for the Relative Scatter Lookup Table. (If you prefer, you can calculate and deduct Lowest Valid Value scatter from each band individually and bypass the Lookup Table, but if you do so, make sure scatter has a high power correlation with band center wavelength - unless you are making a comparison analysis, be consistent with the scatter method used.) The lowest valid band 4 value for the tutorial data is 6447. (The Lowest Valid Value is a from an entire scene; the tutorial data is part of a scene. The Lowest Valid Value of 6447 happens to be from an area of the scene outside the extent of the tutorial data.)
4) Apply the following equation to the scatter DN (the Lowest Valid Value from the red band) from Step 3: ([DN x .00002] - 0.1).
5) Divide the scatter value from Step 4 by the cosine of the solar zenith (0.878335597) to convert to reflectance; the reflectance value of the band 4 starting scatter for the tutorial data is 0.032949.
6) Acquire relative scatter for the visible bands from the Landsat 8 Continuous Relative Scatter Lookup Table and deduct them from the visible band TOA reflectance from Step 2 to calculate surface reflectance.
THE TUTORIAL HAS CHANGED SLIGHTLY AS OF 8/24/16, whereby PM1 SR is now included, instead of PM SR. The PM1 SR technique is the same as PM SR, except PM1 SR includes relative scatter also being deducted from band 5 (NIR). PM1 SR is the original method (posted at least a two years ago) that has relative scatter deducted from bands 2 (blue), 3 (green), and 5 (near infrared) based on the starting scatter from band 4 (red). This is explained more in the next paragraph.
For this tutorial, the scatter values relative to the starting band 4 value of 0.032949 are: 0.08121 (blue), 0.04961 (Green), 0.04149 (Green2), and 0.01895 (NIR). Use the original band 4 value of 0.032949 instead of the slightly different band 4 lookup value 0.03290. Green2 is a relative green scatter value modified slightly from the original scatter table value (though both are listed in the Relative Scatter Table, which was developed well before Landsat 8 surface reflectance was made available by the USGS). Green2 derives PM2 SR values, and is based on the research shown and described in the Landsat 8 SR Comparison page that shows how the modified green values retrieve surface reflectance overall closer to USGS Landsat 8 algorithm green values. PM2 SR also uses Top of Atmosphere (TOA) reflectance for Band 5 (NIR) because USGS Landsat 8 Algorithm band 5 surface reflectance values are nearly identical to TOA. As the PM2 SR method focuses on retrieving values closer to the USGS Landsat 8 algorithm reflectance values, the PM1 SR method focuses on the power relationships between scatter amounts and band center wavelength the should exist (power relationships between scatter and band center wavelength in the Relative Scatter Lookup Table decrease more with PM2 SR as scatter becomes higher). An example of applied PM1 SR can be found on the Wildland Fuel Moisture Content (opens in new window) remote sensing page on this website. Choose the method you prefer based on these main points, but be consistent with the method used.
PLEASE READ THE FOLLOWING REGARDING ONE-PERCENT DARK OBJECT REFLECTANCE, WHICH IS NOT APPLIED FOR LANDSAT 8.
One-Percent Dark Object Reflectance Background
One-percent surface reflectance is the process of deducting .01 from scatter (haze) in order to acquire one-percent reflectance from the established low value. This has been shown to improve accuracy or retrieved surface reflectance when applied to previous Landsats. Analysis here with Landsat 8 shows that it is better to bypass (not apply) this step and simply deduct scatter (haze) from the different bands based on the relative scatter table. This could be due to the fact that Landsat 8 has a much different sensor, the Lowest Valid Value scatter amount is a different method than those used in the past that establishing a lower relative amount (sometime the very lowest value as opposed to a value at the based of an abrupt increase in the histogram), or a combination of the two (or something different).
Tutorial Reflectance Units
(DN values should be converted to the reflectance units below; USGS raster reflectance values are in the native downloaded 4-integer format [divide by 10,000 for reflectance units])
|Landsat 8||USGS SR||PM1 SR||PM2 SR||TOA|
|Landsat 8||Stan. Dev.||Stan. Dev.||Stan. Dev.||Stan. Dev.|