Landsat 9 is planned for launch in December 2020 to continue the mission of observing changes on the Earth’s surface that began in 1972 with the launch of Landsat 1. Like Landsat 8, Landsat 9 will carry two imaging instruments: Operational Land Imager 2 (OLI-2), designed and built by Ball Aerospace**, and Thermal Infrared Sensor 2 (TIRS-2), manufactured by NASA Goddard Space Flight Center (GSFC). As of this writing, both sensors have completed the instrument-level ground testing and are ready for integration into the spacecraft. Data collected during the pre-launch performance testing are analyzed to assess the usability of responses of the video reference pixels (VRPs) located on the focal planes of OLI-2 and Landsat 8 OLI for more accurate detector bias estimates, develop a methodology to correct for nonlinearities in the OLI-2 response and compare it to the OLI correction approach, and determine the spatial performance of TIRS-2.
Landsat data in the U.S. Geological Survey (USGS) archive are being reprocessed to generate a tiered collection of consistently geolocated and radiometrically calibrated products that are suitable for time series analyses. With the implementation of the collection management, no major updates will be made to calibration of the Landsat sensors within a collection. Only calibration parameters needed to maintain the established calibration trends without an effect on derived environmental records will be regularly updated, while all other changes will be deferred to a new collection. This first collection, Collection 1, incorporates various radiometric calibration updates to all Landsat sensors including absolute and relative gains for Landsat 8 Operational Land Imager (OLI), stray light correction for Landsat 8 Thermal Infrared Sensor (TIRS), absolute gains for Landsat 4 and 5 Thematic Mappers (TM), recalibration of Landsat 1-5 Multispectral Scanners (MSS) to ensure radiometric consistency among different formats of archived MSS data, and a transfer of Landsat 8 OLI reflectance based calibration to all previous Landsat sensors. While all OLI/TIRS, ETM+ and majority of TM data have already been reprocessed to Collection 1, a completion of MSS and remaining TM data reprocessing is expected by the end of this year. It is important to note that, although still available for download from the USGS web pages, the products generated using the Pre-Collection processing do not benefit from the latest radiometric calibration updates. In this paper, we are assessing radiometry of solar reflective bands in Landsat Collection 1 products through analysis of trends in on-board calibrator and pseudo invariant site (PICS) responses.
The Landsat Project is planning to implement a new collection management strategy for Landsat products generated at the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center. The goal of the initiative is to identify a collection of consistently geolocated and radiometrically calibrated images across the entire Landsat archive that is readily suitable for time-series analyses. In order to perform an accurate land change analysis, the data from all Landsat sensors must be on the same radiometric scale. Landsat 7 Enhanced Thematic Mapper Plus (ETM+) is calibrated to a radiance standard and all previous sensors are cross-calibrated to its radiometric scale. Landsat 8 Operational Land Imager (OLI) is calibrated to both radiance and reflectance standards independently. The Landsat 8 OLI reflectance calibration is considered to be most accurate. To improve radiometric calibration accuracy of historical data, Landsat 1-7 sensors also need to be cross-calibrated to the OLI reflectance scale. Results of that effort, as well as other calibration updates including the absolute and relative radiometric calibration and saturated pixel replacement for Landsat 8 OLI and absolute calibration for Landsat 4 and 5 Thematic Mappers (TM), will be implemented into Landsat products during the archive reprocessing campaign planned within the new collection management strategy. This paper reports on the planned radiometric calibration updates to the solar reflective bands of the new Landsat collection.
The Operational Land Imager (OLI) aboard the LDCM satellite was rigorously radiometrically characterized prior to launch to assure absolute calibration that is NIST traceable. On orbit additional dedicated calibration collects are being made to continue monitoring and characterizing the OLI radiometric performance. In this paper we report on the OLI on-orbit uniformity performance, which is a natural extension of the absolute radiometric accuracy. Such performance characteristic in remote sensing instruments is assuring that the radiometric accuracy in low contrast images is preserved while avoiding non-uniformity artifacts in the produced radiometric product. The LDCM project science team working with the instrument teams developed a performance metric to monitor the uniformity performance. We will describe the uniformity performance metric and discuss associated error sources in obtaining the radiometric calibration parameters that impact the uniformity correction. We will compare the uniformity performance between solar diffuser observation and earth data.
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.
From the Landsat program's inception in 1972 to the present, the earth science user community has benefited from a
historical record of remotely sensed data. The multispectral data from the Landsat 5 (L5) Thematic Mapper (TM) sensor
provide the backbone for this extensive archive. Historically, the radiometric calibration procedure for this imagery used
the instrument's response to the Internal Calibrator (IC) on a scene-by-scene basis to determine the gain and offset for
each detector. The IC system degraded with time causing radiometric calibration errors up to 20 percent. In May 2003
the National Landsat Archive Production System (NLAPS) was updated to use a gain model rather than the scene
acquisition specific IC gains to calibrate TM data processed in the United States. Further modification of the gain model
was performed in 2007. L5 TM data that were processed using IC prior to the calibration update do not benefit from the
recent calibration revisions. A procedure has been developed to give users the ability to recalibrate their existing Level-1
products. The best recalibration results are obtained if the work order report that was originally included in the standard
data product delivery is available. However, many users may not have the original work order report. In such cases, the
IC gain look-up table that was generated using the radiometric gain trends recorded in the NLAPS database can be used
for recalibration. This paper discusses the procedure to recalibrate L5 TM data when the work order report originally
used in processing is not available. A companion paper discusses the generation of the NLAPS IC gain and bias look-up
tables required to perform the recalibration.
The National Landsat Archive Production System (NLAPS) has been the primary processing system for Landsat data
since U.S. Geological Survey (USGS) Earth Resources Observation and Science Center (EROS) started archiving
Landsat data. NLAPS converts raw satellite data into radiometrically and geometrically calibrated products. NLAPS
has historically used the Internal Calibrator (IC) to calibrate the reflective bands of the Landsat-5 Thematic Mapper
(TM), even though the lamps in the IC were less stable than the TM detectors, as evidenced by vicarious calibration
results. In 2003, a major effort was made to model the actual TM gain change and to update NLAPS to use this model
rather than the unstable IC data for radiometric calibration. The model coefficients were revised in 2007 to reflect
greater understanding of the changes in the TM responsivity.
While the calibration updates are important to users with recently processed data, the processing system no longer
calculates the original IC gain or offset. For specific applications, it is useful to have a record of the gain and offset
actually applied to the older data. Thus, the NLAPS calibration database was used to generate estimated daily values for
the radiometric gain and offset that might have been applied to TM data.
This paper discusses the need for and generation of the NLAPS IC gain and offset tables. A companion paper covers the
application of and errors associated with using these tables.
The Thematic Mapper (TM) is a multi-spectral electro-optical sensor featured onboard both the Landsat 4 (L4) and
Landsat 5 (L5) satellites. TM sensors have seven spectral bands with center wavelengths of approximately 0.49, 0.56,
0.66, 0.83, 1.65, 11.5 and 2.21 μm, respectively. The visible near-infrared (VNIR) bands are located on the primary
focal plane (PFP), and two short-wave infrared (SWIR) bands and the thermal infrared (TIR) band are located on the
cold focal plane (CFP). The CFP bands are maintained at cryogenic temperatures of about 91 K, to reduce thermal noise
effects. Due to the cold temperature, an ice film accumulates on the CFP dewar window, which introduces oscillations
in SWIR and an exponential decay in TIR band responses. This process is usually monitored and characterized by the
detector responses to the internal calibrator (IC) lamps and the blackbody. The ice contamination on the dewar window
is an effect of the sensor outgassing in a vacuum of the space environment. Outgassing models have been developed,
which are based on the thin-film optical interference phenomenon. They provide the coefficients for correction for
outgassing effects for the entire mission's lifetime. While the L4 TM ceased imaging in August 1993, the L5 TM
continues to operate even after more than 23 years in orbit. The process of outgassing in L5 TM is still occurring,
though at a much lower rate than during early years of mission. Although the L4 and L5 TM sensors are essentially
identical, they exhibit slightly different responses to the outgassing effects. The work presented in the paper summarizes
the results of modeling outgassing effects in each of the sensors and provides a detailed analysis of differences among
the estimated modeling parameters. For both sensors, water ice was confirmed as a reasonable candidate for
contaminant material, the contaminant growth rate was found to be gradually decreasing with the time since launch, and
the indications exist that some film may remain after the CFP warm-up procedures, which are periodically initiated to
remove accumulated contamination. The observed difference between the models could be contributed to differences in
the operational history for the sensors, the content and amount of contaminant impurities, the sensor spectral filter
responses, and the internal calibrator systems.
The Landsat archive provides more than 35 years of uninterrupted multispectral remotely sensed data of
Earth observations. Since 1972, Landsat missions have carried different types of sensors, from the Return
Beam Vidicon (RBV) camera to the Enhanced Thematic Mapper Plus (ETM+). However, the Thematic
Mapper (TM) sensors on Landsat 4 (L4) and Landsat 5 (L5), launched in 1982 and 1984 respectively, are the
backbone of an extensive archive.
Effective April 2, 2007, the radiometric calibration of L5 TM data processed and distributed by the U.S.
Geological Survey (USGS) Center for Earth Resources Observation and Science (EROS) was updated to use
an improved lifetime gain model, based on the instrument's detector response to pseudo-invariant desert site
data and cross-calibration with the L7 ETM+. However, no modifications were ever made to the radiometric
calibration procedure of the Landsat 4 (L4) TM data. The L4 TM radiometric calibration procedure has
continued to use the Internal Calibrator (IC) based calibration algorithms and the post calibration dynamic
ranges, as previously defined.
To evaluate the "current" absolute accuracy of these two sensors, image pairs from the L5 TM and L4 TM
sensors were compared. The number of coincident image pairs in the USGS EROS archive is limited, so the
scene selection for the cross-calibration studies proved to be a challenge. Additionally, because of the lack of
near-simultaneous images available over well-characterized and traditionally used calibration sites, alternate
sites that have high reflectance, large dynamic range, high spatial uniformity, high sun elevation, and minimal
cloud cover were investigated. The alternate sites were identified in Yuma, Iraq, Egypt, Libya, and Algeria.
The cross-calibration approach involved comparing image statistics derived from large common areas
observed eight days apart by the two sensors. This paper summarizes the average percent differences in
reflectance estimates obtained between the two sensors. The work presented in this paper is a first step in
understanding the current performance of L4 TM absolute calibration and potentially serves as a platform to
revise and improve the radiometric calibration procedures implemented for the processing of L4 TM data.
The Landsat suite of satellites has collected the longest continuous archive of multispectral data of any land observing
space program. From the Landsat program's inception in 1972 to the present, the Earth science
user community has benefited from a historical record of remotely sensed data. However, little attention has
been paid to ensuring that the data are calibrated and comparable from mission to mission. Launched in 1982
and 1984 respectively, the Landsat 4 (L4) and Landsat 5 (L5) Thematic Mappers (TM) are the backbone of an
extensive archive of moderate resolution Earth imagery. To evaluate the "current" absolute accuracy of these
two sensors, image pairs from the L5 TM and L4 TM sensors were compared. The approach involves
comparing image statistics derived from large common areas observed eight days apart by the two sensors.
The average percent differences in reflectance estimates obtained from the L4 TM agree with those from the
L5 TM to within 15 percent. Additional work to characterize the absolute differences between the two sensors
over the entire mission is in progress.
Oscillations in radiometric gains of the short wave infrared (SWIR) bands in Landsat-4 (L4) and Landsat-5 (L5) Thematic Mappers (TMs) are observed through an analysis of detector responses to the Internal Calibrator (IC) pulses. The oscillations are believed to be caused by an interference effect due to a contaminant film buildup on the window of the cryogenically cooled dewar that houses these detectors. This process of contamination, referred to as outgassing effects, has been well characterized using an optical thin-film model that relates detector responses to the accumulated film thickness and its growth rate. The current models for L4 TM are based on average detector responses to the second brightest IC lamp and have been derived from three data sets acquired during different times throughout the instrument's lifetime. Unlike in L5 TM outgassing characterization, it was found that the L4 TM responses to all three IC lamps can be used to provide accurate characterization and correction for outgassing effects. The analysis of single detector responses revealed an up to five percent difference in the estimated oscillating periods and also indicated a gradual variation of contaminant growth rate over the focal plane.
Detector responses to the Internal Calibrator (IC) pulses in the Landsat-4 Thematic Mapper (TM) have been observed to follow an oscillatory behavior. This phenomenon is present only in the Short Wave Infrared (SWIR) bands and has been observed throughout the lifetime of the instrument, which was launched in July 1982 and imaged the Earth's surface until late 1993. These periodic changes in amplitude, which can be as large as 7.5 percent, are known as outgassing effects and are believed to be due to optical interference caused by a gradual buildup of an ice-like material on the window of the cryogenically cooled dewar containing the SWIR detectors. Similar outgassing effects in the Landsat-5 TM have been characterized using an optical thin-film model that relates detector behavior to the ice film growth rate, which was found to gradually decrease with time. A similar approach, which takes into consideration the different operational history of the instrument, has been applied in this study to three closely sampled data sets acquired throughout the lifetime of the Landsat-4 TM. Although Landsat-4 and Landsat-5 Thematic Mappers are essentially identical instruments, data generated from analyses of outgassing effects indicate subtle, but important, differences between the two. The estimated lifetime model could improve radiometric accuracy by as much as five percent.
The ability to detect and quantify changes in the Earth's environment depends on satellites sensors that can provide calibrated, consistent measurements of Earth's surface features through time. A critical step in this process is to put image data from subsequent generations of sensors onto a common radiometric scale. To evaluate Landsat-5 (L5) Thematic Mapper's (TM) utility in this role, image pairs from the L5 TM and Landsat-7 (L7) Enhanced Thematic Mapper Plus (ETM+) sensors were compared. This approach involves comparison of surface observations based on image statistics from large common areas observed eight days apart by the two sensors. The results indicate a significant improvement in the consistency of L5 TM data with respect to L7 ETM+ data, achieved using a revised Look-Up-Table (LUT) procedure as opposed to the historical Internal Calibrator (IC) procedure previously used in the L5 TM product generation system. The average percent difference in reflectance estimates obtained from the L5 TM agree with those from the L7 ETM+ in the Visible and Near Infrared (VNIR) bands to within four percent and in the Short Wave Infrared (SWIR) bands to within six percent.