The Thermal Infrared Sensor (TIRS) instrument is the thermal-band imager on the Landsat-8 platform. The initial onorbit calibration estimates of the two TIRS spectral bands indicated large average radiometric calibration errors, -0.29 and -0.51 W/m2 sr μm or -2.1K and -4.4K at 300K in Bands 10 and 11, respectively, as well as high variability in the errors, 0.87K and 1.67K (1-σ), respectively. The average error was corrected in operational processing in January 2014, though, this adjustment did not improve the variability. The source of the variability was determined to be stray light from far outside the field of view of the telescope. An algorithm for modeling the stray light effect was developed and implemented in the Landsat-8 processing system in February 2017. The new process has improved the overall calibration of the two TIRS bands, reducing the residual variability in the calibration from 0.87K to 0.51K at 300K for Band 10 and from 1.67K to 0.84K at 300K for Band 11. There are residual average lifetime bias errors in each band: 0.04 W/m2 sr μm (0.30K) and -0.04 W/m2 sr μm (-0.29K), for Bands 10 and 11, respectively.
KEYWORDS: Landsat, Calibration, Imaging systems, Signal to noise ratio, Aerosols, Space operations, Earth observing sensors, Current controlled current source
The Landsat 8 Operational Land Imager (OLI) impressed science users soon after launch in early 2013 with both its radiometric and geometric performance. After three years on-orbit, OLI continues to exceed expectations with its high signal-to-noise ratio, low striping, and stable response. The few artifacts that do exist, such as ghosting, continue to be minimal and show no signs of increasing. The on-board calibration sources showed a small decrease in response during the first six months of operations in the coastal aerosol band, but that decrease has stabilized to less than a half percent per year since that time. The other eight bands exhibit very little change over the past three years and have remained well within a half percent of their initial response to all on-board calibration sources. Analysis of lunar acquisitions also agree with the on-board calibrators. Overall, the OLI on-board the Landsat 8 spacecraft continues to provide exceptional measurements of the Earth's surface to continue the long tradition of Landsat.
Landsat 8 and its two Earth imaging sensors, the Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) have been operating on-orbit for 2 ½ years. Landsat 8 has been acquiring substantially more images than initially planned, typically around 700 scenes per day versus a 400 scenes per day requirement, acquiring nearly all land scenes. Both the TIRS and OLI instruments are exceeding their SNR requirements by at least a factor of 2 and are very stable, degrading by at most 1% in responsivity over the mission to date. Both instruments have 100% operable detectors covering their cross track field of view using the redundant detectors as necessary. The geometric performance is excellent, meeting or exceeding all performance requirements. One anomaly occurred with the TIRS Scene Select Mirror (SSM) encoder that affected its operation, though by switching to the side B electronics, this was fully recovered. The one challenge is with the TIRS stray light, which affects the flat fielding and absolute calibration of the TIRS data. The error introduced is smaller in TIRS band 10. Band 11 should not currently be used in science applications.
Landsat-8 and its two Earth imaging sensors, the Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) have been operating on-orbit for 2 1/2 years. The OLI radiometric calibration, which is monitored using on-board lamps, on-board solar diffusers, the moon and vicarious calibration techniques has been stable to within 1% over this period of time. The Coastal Aerosol band, band 1, shows the largest change at about 1% over the period; all other bands have shown no significant trend. OLI bands 1- 4 show small discontinuities in response (+0.1% to 0.2%) beginning about 7 months after launch and continuing for about 1 month associated with a power cycling of the instrument, though the origin of the recovery is unclear. To date these small changes have not been compensated for, but this will change with a reprocessing campaign that is currently scheduled for Fall 2015. The calibration parameter files (each typically covering a 3 month period) will be updated for these observed gain changes. A fitted response to an adjusted average of the lamps, solar and lunar results will represent the trend, sampled at the rate of one value per CPF.
KEYWORDS: Calibration, Sensors, Earth observing sensors, Data conversion, Image processing, Observatories, Landsat, Space operations, Data processing, Short wave infrared radiation
Shortly after Landsat-8 launched in February 2013, the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center began creating radiometrically and geometrically corrected products. In order to provide these products as soon as possible, the Landsat Product Generation System (LPGS) was developed based on instrument designs and testing prior to launch. While every effort was made to ensure the LPGS produces highly accurate products, some aspects of the sensors are difficult to characterize during testing on the ground. Examples of these characteristics include differences between individual detectors that make up the focal plane array, and the way detectors view radiometric targets in preflight testing versus the way they view the Earth on orbit, and the accuracy of the measurements made on the ground. Once in orbit, more accurate measurements of these sensor characteristics were made that improved processing parameters, resulting in improved quality of the final imagery. This paper reviews the changes that have occurred to the processing of Landsat-8 data products which include parameter changes as well as some modifications to the processing system itself. These changes include: improved linearization of the data, both to parameters and the algorithm used for linearizing the data; improved radiance and reflectance conversion coefficients; individual detector coefficients to improve uniformity; and geometric alignment coefficients to improve the geometric accuracy. These improvements lead to a reprocessing campaign that occurred in early in 2014 that replaced all prior data with improved products.
The Landsat 8 satellite was launched on February 11, 2013, to systematically collect multispectral images for detection and quantitative analysis of changes on the Earth’s surface. The collected data are stored at the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center and continue the longest archive of medium resolution Earth images. There are two imaging instruments onboard the satellite: the Operational Land Imager (OLI) and the Thermal InfraRed Sensor (TIRS). This paper summarizes radiometric performance of the OLI including the bias stability, the system noise, saturation and other artifacts observed in its data during the first 1.5 years on orbit. Detector noise levels remain low and Signal-To-Noise Ratio high, largely exceeding the requirements. Impulse noise and saturation are present in imagery, but have negligible effect on Landsat 8 products. Oversaturation happens occasionally, but the affected detectors quickly restore their nominal responsivity. Overall, the OLI performs very well on orbit and provides high quality products to the user community.
The Landsat Data Continuity Mission (LDCM) is planning to launch the Landsat 8 satellite in December 2012, which
continues an uninterrupted record of consistently calibrated globally acquired multispectral images of the Earth started in
1972. The satellite will carry two imaging sensors: the Operational Land Imager (OLI) and the Thermal Infrared Sensor
(TIRS). The OLI will provide visible, near-infrared and short-wave infrared data in nine spectral bands while the TIRS
will acquire thermal infrared data in two bands. Both sensors have a pushbroom design and consequently, each has a
large number of detectors to be characterized.
Image and calibration data downlinked from the satellite will be processed by the U.S. Geological Survey (USGS) Earth
Resources Observation and Science (EROS) Center using the Landsat 8 Image Assessment System (IAS), a component
of the Ground System. In addition to extracting statistics from all Earth images acquired, the IAS will process and trend
results from analysis of special calibration acquisitions, such as solar diffuser, lunar, shutter, night, lamp and blackbody
data, and preselected calibration sites. The trended data will be systematically processed and analyzed, and calibration
and characterization parameters will be updated using both automatic and customized manual tools. This paper describes
the analysis tools and the system developed to monitor and characterize on-orbit performance and calibrate the Landsat 8
sensors and image data products.
The Operational Land Imager (OLI) is a pushbroom sensor that will be a part of the Landsat Data Continuity Mission
(LDCM). This instrument is the latest in the line of Landsat imagers, and will continue to expand the archive of
calibrated earth imagery. An important step in producing a calibrated image from instrument data is accurately
accounting for the bias of the imaging detectors. Bias variability is one factor that contributes to error in bias estimation
for OLI. Typically, the bias is simply estimated by averaging dark data on a per-detector basis. However, data acquired
during OLI pre-launch testing exhibited bias variation that correlated well with the variation in concurrently collected
data from a special set of detectors on the focal plane. These detectors are sensitive to certain electronic effects but not
directly to incoming electromagnetic radiation. A method of using data from these special detectors to estimate the bias
of the imaging detectors was developed, but found not to be beneficial at typical radiance levels as the detectors respond
slightly when the focal plane is illuminated. In addition to bias variability, a systematic bias error is introduced by the
truncation performed by the spacecraft of the 14-bit instrument data to 12-bit integers. This systematic error can be
estimated and removed on average, but the per pixel quantization error remains. This paper describes the variability of
the bias, the effectiveness of a new approach to estimate and compensate for it, as well as the errors due to truncation
and how they are reduced.
The Advanced Land Imager (ALI) was developed as a prototype sensor for follow on missions to Landsat-7. It was launched in November 2000 on the Earth Observing One (EO-1) satellite as a nominal one-year technology demonstration mission. As of this writing, the sensor has continued to operate in excess of 5 years. Six of the ALI's nine multi-spectral (MS) bands and the panchromatic band have similar spectral coverage as those on the Landsat-7 ETM+. In addition to on-board lamps, which have been significantly more stable than the lamps on ETM+, the ALI has a solar diffuser and has imaged the moon monthly since launch. This combined calibration dataset allows understanding of the radiometric stability of the ALI system, its calibrators and some differentiation of the sources of the changes with time. The solar dataset is limited as the mechanism controlling the aperture to the solar diffuser failed approximately 18 months after launch. Results over 5 years indicate that: the shortest wavelength band (443 nm) has degraded in response about 2%; the 482 nm and 565 nm bands decreased in response about 1%; the 660 nm, 790 nm and 868 nm bands each degraded about 5%; the 1250 nm and 1650 nm bands did not change significantly and the 2215 nm band increased in response about 2%.
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