On February 3, 2014, the entire Landsat 8 archive will be cleared from the online cache and reprocessed to take advantage of calibration improvements identified during its first year of operation. All Landsat 8 scenes will be removed from the online cache at this time and these data will be reprocessed starting with the most recent acquisitions and proceeding back to the beginning of the mission. Data will then become available for download. Scenes waiting to be reprocessed will also be available for on-demand product orders. Reprocessing is expected to take approximately 50 days.
The Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) instruments onboard the satellite have proven to be outstanding sensors; however, all sensors have required radiometric and geometric refinements to ensure good calibration and data continuity. This reprocessing campaign includes all previously implemented calibration parameter updates implemented since launch. These changes are described in more detail below.
Changes to Operational Land Imager (OLI) data
All spectral bands of the OLI sensor have shown minor striping, noticeable primarily in dark uniform areas; the striping is worse in coastal aerosol (CA) and short wave infrared (SWIR) bands. Striping has been reduced by making refinements to the detector linearization correction in the Radiometric Look-Up Table (RLUT). The relative radiometric accuracy is improved by this change; however, the absolute accuracy remains unchanged.
An additional change to the relative gains in the Calibration Parameter File (CPF) will be updated to further reduce striping in the cirrus band. This change will not affect the absolute radiometric accuracy.
The OLI radiometric calibration is being updated to reflect better knowledge of the prelaunch test data, on which the original calibration was based. The reflectance will change at most 0.8 percent, except for the cirrus Band 9, which will change by 7.3 percent (see table). This calibration update will make the reflectance appear brighter than when these data were processed with the previous radiometric calibration. These changes apply only to data converted to reflectance. An improvement to the absolute accuracy of the radiance values, around 2 percent for most bands, will also be implemented.
|OLI Bands||Radiance Change (%)||Reflectance Change (%)|
|1 (Coastal Aerosol)||-2.1||0.8|
Table 1: OLI Radiance and Reflective Changes
Changes to Thermal Infrared Sensor (TIRS) data
The TIRS temperature offsets noted on November 14, 2013 Calibration Notice on http://landsat.usgs.gov/calibration_notices.php is a primary driver for this reprocessing effort.
These offsets remove 0.29 W/m2/sr/um (~2.1 K) from Band 10 and 0.51 W/m2/sr/um (~4.4 K) from band 11, relative to products processed prior to February 3, 2014. The offsets represent an average error introduced by stray light coming from outside the TIRS field of view and will improve the data accuracy for typical growing season data (10° to 30° C) where the surrounding areas are similar in temperature.
The Root Mean Square (RMS) variability of this correction is 0.12 W/m2/sr/um (~0.8 K) for Band 10 and remains greater at 0.2 W/m2/sr/um (~1.75 K) for Band 11. Due to the larger calibration uncertainty associated with Band 11, it is recommended that users refrain from relying on Band 11 data in quantitative analysis of the TIRS data, such as the use of split window techniques for atmospheric correction and retrieval of surface temperature values.
|TIRS Bands||Radiance Offset
[K @ 300K]
|10||-0.29 +/- 0.12||-2.1 +/- 0.8|
|11||-0.51 +/- 0.2||-4.4 +/- 1.75|
Table 2: TIRS offset changes
Geometric Alignment between the Sensors
There are a few geometric changes that will also be fixed in the reprocessing. Based on the analysis of on-orbit data, the alignment between the TIRS instrument and the OLI instrument will be adjusted according to these time periods:
|Effective Date Range||Change in TIRS alignment||Change in TIRS alignment|
|12 microradians||8.5 meters|
|25 microradians||18 meters|
|10 microradians||7.1 meters|
Table 3: Geometric alignment changes
There is no change to the TIRS alignment in products after the calibration update on November 27, 2013, which already accounted for this adjustment. These adjustments will improve the alignment of the TIRS thermal bands to the OLI reflective bands.
Due to an apparent seasonal variation in the common alignment of the OLI and TIRS instruments to the Landsat 8 spacecraft attitude control system, a sensor alignment update has been applied to both instruments effective October 1, 2013. The magnitude of this change is approximately 12 microradians (8.5 meters) across track and 8 microradians (6 meters) along track. This change does not impact precision Level 1T (L1T) products (which are corrected using ground control points) but will change the geolocation of systematic Level 1GT (L1GT) products.
New Ground Control Points (GCPs) will become available for three WRS-2 path/rows and GCPs contained within large water bodies will be removed on February 3, 2014 to coincide with the Landsat 8 archive reprocessing. As a consequence of the improved GCPs, scenes once created as a L1GT product may now process to a L1T product. The January 16, 2014 Landsat mission headlines and calibration notices detail this update: http://landsat.usgs.gov/calibration_notices.php.
In addition to the details provided above, the changes noted in the January 6, 2014 Calibration Notice (found the website above) will also be included in this reprocessing.
An incorrect bias adjustment for Thermal Infrared Sensor (TIRS) data was discovered in the latest release of the Landsat 8 processing system, which has caused a significant error in the TIRS products produced from Landsat 8 scenes acquired from January 14, 2014 to January 23, 2014. (The Operational Land Imager (OLI) bands are not affected.) All Landsat 8 scenes processed between January 14 and January 23 will be purged from the online cache and will become available for on demand order processing. An estimated 3 percent absolute radiometric error is observed and the errors do cause significant striping and banding in bands 10 and 11.
The screenshot below shows a scene processed with the incorrect bias parameters on the left and as it should appear on the right.
Figure 1: Image displaying incorrect bias adjustment (left), and corrected (right)
New Ground Control Points (GCPs) will become available for three WRS-2 path/rows listed below on February 3, 2014 to coincide with the Landsat 8 archive reprocessing:
Because these GCPs are more accurate than previous versions, users should consider replacing Landsat 8 images downloaded before February 3rd, 2014. It is recommended that previously downloaded images for these paths/rows be re-ordered to employ the new GCPs, as scenes once created as a systematic Level 1GT (L1GT) product may now process to a precision Level 1T (L1T) product.
Additionally, GCPs that were determined to be contained within large bodies of water were removed from use during Level 1 processing. Although the presence of these points typically has little effect on the quality of the geometric registration of the L1T imagery, there have been cases where the removal of these GCPs changes the product type from L1GT to L1T.
Several calibration parameter updates will be implemented as part of the Landsat 8 data reprocessing on February 3, 2014 that will result in improved product quality. This reprocessing campaign includes all previously implemented calibration parameter updates that have been implemented since launch. These changes are described in more detail below.
The OLI detector linearization correction coefficients have been refined for all spectral bands to decrease striping in imagery over dark uniform areas. The absolute radiometric accuracy is not significantly affected.
The OLI radiance conversion coefficients are also improved slightly by correcting for a slight error in pre-launch calibration that resulted in product radiance values with as much as a +2% error. A slight improvement to the absolute accuracy of the reflectance values, mainly the cirrus band, will also be implemented. The relative gains will also be updated to reduce striping in the cirrus band, but this will not affect the absolute radiometric accuracy.
The previously mentioned TIRS temperature offset (See the November 15, 2013 Notice) will also be implemented on February 3, 2014. These offsets remove 0.29 W/m^2/sr/um from TIRS band 10 and 0.51 W/m^2/sr/um from TIRS band 11, relative to products processed prior to February 3, 2014. These offsets will remove an average error introduced by stray light coming from outside the TIRS field of view and will improve the data accuracy for typical growing season data (10° to 30° C) where the surrounding areas are similar in temperature. The RMS variability of this correction is 0.12 W/m^2/sr/um for TIRS band 10 and but remains greater at 0.2 W/m^2/sr/um for TIRS band 11. Due to the larger calibration uncertainty associated with TIRS band 11, it is recommended that users refrain from relying on band 11 data in quantitative analysis of the TIRS data, such as the use of split window techniques for atmospheric correction and retrieval of surface temperature values.
Based on the analysis of on-orbit data, the alignment between the TIRS instrument and the OLI instrument will be adjusted according to these time periods:
Effective Date Range
Change in TIRS alignment
There is no change to the TIRS alignment in products after the calibration update on November 27, 2013, which already accounted for this adjustment.
The majority of the radiometric calibration changes indicated in the October 25, 2013 calibration notice have been deferred to early-2014, to coincide with a software update for the Landsat Product Generation System (LPGS). Therefore, reprocessing of the entire Landsat 8 archive will not occur before early-2014.
When the reprocessing effort begins, the OLI radiance-to-reflectance conversion coefficients will be adjusted for the cirrus band (Band 9) to account for on-orbit performance. The prelaunch derived coefficients were calculated using heliostat measurements, which were expected to be in error because little sunlight reaches the ground at these wavelengths. This adjustment changes the reflectance by about 7 percent in the cirrus band. Additionally, the precision of the other spectral bands’ radiance-to-reflectance conversion coefficients will be increased, changing the reflectance by up to 0.3 percent.
Relating to TIRS thermal band calibration, prior to the early-2014 update, users may subtract 0.29 W/(m2 sr µm) from every TIRS Band 10 calibrated radiance value, and 0.51 W/(m2 sr µm) for every TIRS Band 11 calibrated radiance value to provide values closer (on average) to the actual radiances. The equations to convert from calibrated product pixel values to calibrated radiance values can be found here (http://landsat.usgs.gov/Landsat8_Using_Product.php). These numbers are based on comparisons to surface water temperatures and correspond to a -2.1 K correction (Band 10) and a -4.4 K correction (Band 11) for a 295 K brightness temperature. The rms variability in the required adjustment is roughly 0.12 W/(m2 sr µm) (0.8 K) for Band 10 and 0.2 W/(m2 sr µm) (1.75 K) for Band 11. Studies indicate that the errors are scene dependent and probably related to out-of-field response in the TIRS instrument.
Given the larger uncertainty in the Band 11 values, users should work with TIRS Band 10 data as a single spectral band (like Landsat 7 Enhanced Thematic Mapper Plus (ETM+)) and should not attempt a split-window correction using both TIRS Bands 10 and 11.
Updates will be provided on this page as understanding of the calibration improves, and also when the reprocessing effort is planned to begin.
In the near future, calibration changes will be made that will affect the Thermal Infrared Sensor (TIRS) Band 10 and all of the Operational Land Imager (OLI) bands onboard Landsat 8.
The calibration for TIRS Band 10 will be lowered by a constant 0.32 W/(m2 sr µm) for every TIRS Band 10 pixel. This adjustment is being made due to significant discrepancies as compared to surface water temperature measurements. Studies are ongoing to better characterize the source of the calibration errors, and if possible, provide a more accurate scene-dependent correction. No adjustment will be made to TIRS Band 11, as indications are that its calibration is further off and more variable. Until indicated otherwise, users should work with TIRS Band 10 data as a single spectral band (like Landsat 7 Enhanced Thematic Mapper Plus (ETM+)) and should not attempt a split-window correction using both TIRS Bands 10 and 11.
Prior to this reprocessing effort, users can subtract 0.32 W/(m2 sr µm) from the TIRS Band 10 Top-of-Atmosphere (TOA) radiance data to improve the accuracy of their current image products or to avoid downloading a new image product after reprocessing occurs. Once a more accurate scene-dependent correction is determined, a second purge and reprocessing will take place.
The OLI radiance-to-reflectance conversion coefficients will be adjusted for the cirrus band (Band 9) to account for on-orbit performance. The prelaunch derived coefficients were calculated using heliostat measurements, which were expected to be in error because little sunlight reaches the ground at these wavelengths. This adjustment changes the reflectance by about 7 percent in the cirrus band. Additionally, the precision of the other spectral bands’ radiance-to-reflectance conversion coefficients will be increased, changing the reflectance by up to 0.3 percent.
The relative gains of single detectors on the edges of each OLI Sensor Chip Assembly (SCA) will be updated to correct slight striping that is typically not visible. This update will affect all OLI spectral bands.
On September 19, 2013 (DOY 262) at approximately 20:08 UTC, Landsat 8 experienced an unplanned transition to safe hold following an attitude control anomaly. Precision attitude control was recovered and imaging operations resumed on day of year 264 (September 21, 2013). Post-anomaly calibration checks detected a systematic change in the alignment between the OLI and TIRS sensors. No change in the OLI alignment to the spacecraft attitude control system was apparent so the shift is being attributed to the TIRS instrument.
The magnitude of the change – a pitch axis offset of approximately 30 microradians (about 0.2 TIRS pixels) – is large enough to threaten the thermal-to-reflective band registration requirements. Band registration tests confirm that the along-track TIRS-to-OLI band registration performance has been degraded since the safe hold event.
A calibration parameter file (CPF) update to the ACS_to_TIRS_Rotation_Matrix parameter was developed to correct this offset and was put into production on September 27, 2013. This update is effective from September 21, 2013, so a subdivision of the 3rd quarter CPF effective date range will be required. The new parameters will also be used for the upcoming 4th quarter CPF unless the ongoing monitoring of TIRS-to-OLI alignment indicates that further changes are required.
No direct cause for the alignment change is known but it may be related to the change in the spacecraft thermal environment during the safe hold period. If this is the case, it is possible that, over time, the alignment will drift back closer to its earlier position.
Discrepancies have been noted between calibrated Landsat 8 TIRS Bands 10 and 11 data, and surface-water temperature measurements collected to validate thermal band calibration.
Surface-water temperatures derived from TIRS data, after correction for atmospheric transmission and emissivity, are warmer than measured surface-water temperatures by 2K or more. These discrepancies also may not be consistent across the focal plane. This indicates a possible bias or other error in TIRS calibration that places the calibration uncertainty beyond the specified performance of 2 percent.
Users are cautioned to be aware of potential impacts to their analyses and results. The calibration team continues to analyze TIRS data and compare results to surface-water temperature measurements to discover the source of the discrepancy.
Updates to TIRS calibration coefficients will be incorporated into Landsat 8 data processing as soon as the discrepancy is sufficiently understood. Details will be provided on this website as they become available.
An update to the CPF on August 21, 2013 improves the geodetic consistency with Landsat 1-7 imagery. Due to some GLS 2000 scenes having significant geodetic errors, a limit is set between the systematically corrected product and the GLS 2000 reference. This limit has been increased from 100 meters and is now set at 200 meters. Scenes with a difference less than 200 meters will be consistent with historical Landsat imagery. There are no known GLS 2000 reference scenes that are off more than 200 meters.
This update also improves the OLI relative calibration which reduces striping in very uniform scenes. The largest improvement is in the Coastal Aerosol (Band 1) where the magnitude of the striping is largest (see figures below), but all reflective bands are affected. The radiometric accuracy has not been affected since these changes are relative to the existing absolute calibration. The banding visible in the figures below is not affected, but will be addressed in a future calibration update.
Figure 1: Band 1. Previous CPF (left); Updated CPF (right). Each image has been radiometrically stretched to show the effect of the updated calibration parameters. Striping has been reduced in the right image, but banding remains the same.
Figure 2: Full resolution zoom of band 1. Previous CPF (left); Updated CPF (right). Each image has been radiometrically stretched to show the effect of the updated calibration parameters. The banding becomes more defined on the right since the striping has been reduced.
Response Linearization Look Up Tables (RLUT) are additional files that accompany Calibration Parameter Files (CPF) and contain parameters used to linearize the output of the OLI detectors. This is done to correct the relationship between Digital Number (DN) values and the dynamic range of the instrument. Linearization also helps to limit saturated pixels to true saturations, and on the dark end, limit zero values to missing data.
An update to the RLUT on August 9, 2013 decreases the striping that was initially seen within the Coastal Aerosol (Band 1), SWIR1 (Band 6), and SWIR2 (Band 7) spectral bands of some Landsat 8 scenes (see figures 1 and 2 below).
The magnitude of these stripes is small and vary based on the brightness of the scene. This improvement will be seen in very uniform areas; however this update may increase the striping and banding slightly in extremely uniform areas of very low reflectance scenes ( < 0.1% reflectance; see figure 3 below). This will be corrected with a future system release.
Figure 1: Band 6 (~5% reflectance). Original RLUT inputs (left); Updated RLUT inputs (right). Each image has been radiometrically stretched to show the effect of the updated calibration parameters.
Figure 2: Band 7 (~5% reflectance). Original RLUT inputs (left); Updated RLUT inputs (right). Each image has been radiometrically stretched to show the effect of the updated calibration parameters.
Figure 3: Band 6 (~0.1% reflectance). Original RLUT inputs (left); Updated RLUT inputs (right). Each image has been radiometrically stretched to show the effect of the updated calibration parameters.