The MODerate-resolution Imaging Spectroradiometer (MODIS) is one of the primary instruments in the National Aeronautics and Space Administration (NASA) Earth Observing System (EOS). The first MODIS instrument was launched in December 1999 on-board the Terra spacecraft. A follow on MODIS was launched on an afternoon orbit in 2002 and is aboard the Aqua spacecraft. Both MODIS instruments are very akin, has 36 bands, among which bands 20 to 25 are Middle Wave Infrared (MWIR) bands covering a wavelength range from approximately 3.750 μm to 4.515 μm. It was found that there was severe contamination in these bands early in mission but the effect has not been characterized and mitigated at the time. The crosstalk effect induces strong striping in the Earth View (EV) images and causes significant retrieval errors in the EV Brightness Temperature (BT) in these bands. An algorithm using a linear approximation derived from on-orbit lunar observations has been developed to correct the crosstalk effect and successfully applied to mitigate the effect in both Terra and Aqua MODIS Long Wave Infrared (LWIR) Photovoltaic (PV) bands. In this paper, the crosstalk effect in the Aqua MWIR bands is investigated and characterized by deriving the crosstalk coefficients using the scheduled Aqua MODIS lunar observations for the MWIR bands. It is shown that there are strong crosstalk contaminations among the five MWIR bands and they also have significant crosstalk contaminations from Short Wave Infrared (SWIR) bands. The crosstalk correction algorithm previously developed is applied to correct the crosstalk effect in these bands. It is demonstrated that the crosstalk correction successfully reduces the striping in the EV images and improves the accuracy of the EV BT in the five bands as was done similarly for LWIR PV bands. The crosstalk correction algorithm should thus be applied to improve both the image quality and radiometric accuracy of the Aqua MODIS MWIR bands Level 1B (L1B) products.
MODerate resolution Imaging Spectroradiometer (MODIS), a remarkable heritage sensor in the fleet of Earth Observing System for the National Aeronautics and Space Administration (NASA) is in space orbit on two spacecrafts. They are the Terra (T) and Aqua (A) platforms which tracks the Earth in the morning and afternoon orbits. T-MODIS has continued to operate over 15 years easily surpassing the 6 year design life time on orbit. Of the several science products derived from MODIS, one of the primary derivatives is the MODIS Cloud Mask (MOD035). The cloud mask algorithm incorporates several of the MODIS channels in both reflective and thermal infrared wavelengths to identify cloud pixels from clear sky. Two of the thermal infrared channels used in detecting clouds are the 6.7 μm and 8.5 μm. Based on a difference threshold with the 11 μm channel, the 6.7 μm channel helps in identifying thick high clouds while the 8.5 μm channel being useful for identifying thin clouds. Starting 2010, it had been observed in the cloud mask products that several pixels have been misclassified due to the change in the thermal band radiometry. The long-term radiometric changes in these thermal channels have been attributed to the electronic crosstalk contamination. In this paper, the improvement in cloud detection using the 6.7 μm and 8.5 μm channels are demonstrated using the electronic crosstalk correction. The electronic crosstalk phenomena analysis and characterization were developed using the regular moon observation of MODIS and reported in several works. The results presented in this paper should significantly help in improving the MOD035 product, maintaining the long term dataset from T-MODIS which is important for global change monitoring.
It has been found that there is severe electronic noise in the Terra Moderate Resolution Imaging Spectroradiometer (MODIS) bands 27-30 which corresponds to wavelengths ranging between 6.7 μm to 9.73 μm. The cause for the issue has been identified to be crosstalk, which is significantly amplified since 2010 due to severe degradation in the electronic circuitry. The crosstalk effect causes unexpected discontinuity/change in the calibration coefficients and induces strong striping artifacts in the earth view (EV) images. Also it is noticed, that there are large long-term drifts in the EV brightness temperature (BT) in these bands. An algorithm using a linear approximation derived from on-orbit lunar observations has been developed to correct the crosstalk effect for them. It was demonstrated that the crosstalk correction can remarkably minimize the discontinuity/change in the calibration coefficients, substantially reduce the striping in the EV images, and significantly remove the long-term drift in the EV BT in all these bands. In this paper, we present the recent progresses in the crosstalk effect analysis and its mitigation. In addition, we will show that besides these four bands, the TEBs in other satellite remote sensors also have significant crosstalk contaminations. Further, it will be demonstrated that the crosstalk correction algorithm we developed can be successfully applied to all the contaminated TEBs to significantly reduce the crosstalk effects and substantially improve both the image quality and the radiometric accuracy of Level-1B (L1B) products for the bands.
MODerate resolution Imaging Spectroradiometer (MODIS), a leading heritage sensor in the fleet of Earth Observing System for the National Aeronautics and Space Administration (NASA) is in space orbit on two spacecrafts. They are the Terra (T) and Aqua (A) platforms. Both instruments have successfully continued to operate beyond the 6 year design life time, with the T-MODIS currently functional beyond 15 years and the A-MODIS operating beyond 13 years respectively. The MODIS sensor characteristics include a spectral coverage from 0.41 μm – 14.4 μm, of which wavelengths ranging from 3.7 μm – 14. 4 μm cover the thermal infrared region also referred to as the Thermal Emissive Bands (TEBs). The TEBs is calibrated using a v-grooved BlackBody (BB) whose temperature measurements are traceable to the National Institute of Standards and Technology temperature scales. The TEBs calibration based on the onboard BB is extremely important for its high radiometric fidelity. In this paper, we provide a complete characterization of the lifetime instrument performance of both MODIS instruments in terms of the sensor gain, the Noise Equivalent difference Temperature, key instrument telemetry such as the BB lifetime trends, the instrument temperature trends, the Cold Focal Plane telemetry and finally, the total assessed calibration uncertainty of the TEBs.
The S-NPP Visible Infrared Imaging Radiometer Suite (VIIRS) instrument is designed based on MODIS heritage and uses a similar on-board calibrating source - a V-grooved blackbody for the Thermal Emissive Bands (TEBs). Except for the 10.7 μm band, the central wavelengths of the rest of the VIIRS TEBs match well with MODIS. To ensure the continuity and consistency of data records between VIIRS and MODIS TEBs, it is important to assess any systematic differences between the two instruments for scenes with temperatures significantly lower than blackbody operating temperatures at ~290 K. In previous studies, the MODIS Calibration and Characterization Support Team (MCST) at NASA/GSFC uses recurrent observations of Dome C, Antarctica by both Terra and Aqua MODIS over the mission lifetime to track their calibration stability and consistency. Near-surface temperature measurements from an Automatic Weather Station (AWS) provide a proxy reference useful for tracking the stability and determining the relative bias between the two MODIS instruments. In this study, the same approach is applied to VIIRS TEBs and the results are compared with those from the matched MODIS TEBs. The results of this study provide a quantitative assessment for VIIRS TEBs performance over the first three years of the mission.
The MODerate-resolution Imaging Spectroradiometer (MODIS) is a legacy Earth remote sensing instrument in the National Aeronautics and Space Administration (NASA) Earth Observing System (EOS). The first MODIS instrument was launched in December 1999 on board the Terra spacecraft. MODIS has 36 bands, among which bands 20-25 and bands 27-36 are thermal emissive bands covering a wavelength range from 3.7μm to 14.2μm. It has been found that there are severe contaminations in Terra bands 27-30 (6.7 μm – 9.73 μm) due to crosstalk of signals among themselves. The crosstalk effect induces strong striping artifacts in the Earth View (EV) images and causes large long-term drifts in the EV brightness temperature (BT) in these bands. An algorithm using a linear approximation derived from on-orbit lunar observations has been developed to correct the crosstalk effect for them. It was demonstrated that the crosstalk correction can substantially reduce the striping noise in the EV images and significantly remove the long-term drifts in the EV BT in the Long Wave InfraRed (LWIR) water vapor channels (bands 27-28). In this paper, the crosstalk correction algorithm previously developed is applied to correct the crosstalk effect in the remaining LWIR bands 29 and 30. The crosstalk correction successfully reduces the striping artifact in the EV images and removes long-term drifts in the EV BT in bands 29-30 as was done similarly for bands 27-28. The crosstalk correction algorithm can thus substantially improve both the image quality and the radiometric accuracy of the Level 1B (L1B) products of the LWIR PV bands, bands 27-30. From this study it is also understood that other Terra MODIS thermal emissive bands are contaminated by the crosstalk effect and that the algorithm can be applied to these bands for crosstalk correction.
The MODerate-resolution Imaging Spectroradiometer (MODIS) is one of the primary instruments in the fleet of NASA’s Earth Observing Systems (EOS) in space. Terra MODIS has completed 15 years of operation far exceeding its design lifetime of 6 years. The MODIS Level 1B (L1B) processing is the first in the process chain for deriving various higher level science products. These products are used mainly in understanding the geophysical changes occurring in the Earth’s land, ocean, and atmosphere. The L1B code is designed to carefully calibrate the responses of all the detectors of the 36 spectral bands of MODIS and provide accurate L1B radiances (also reflectances in the case of Reflective Solar Bands). To fulfill this purpose, Look Up Tables (LUTs), that contain calibration coefficients derived from both on-board calibrators and Earth-view characterized responses, are used in the L1B processing. In this paper, we present the implementation mechanism of the electronic crosstalk correction in the Photo Voltaic (PV) Long Wave InfraRed (LWIR) bands (Bands 27-30). The crosstalk correction involves two vital components. First, a crosstalk correction modular is implemented in the L1B code to correct the on-board Blackbody and Earth-View (EV) digital number (dn) responses using a linear correction model. Second, the correction coefficients, derived from the EV observations, are supplied in the form of LUTs. Further, the LUTs contain time stamps reflecting to the change in the coefficients assessed using the Noise Equivalent difference Temperature (NEdT) trending. With the algorithms applied in the MODIS L1B processing it is demonstrated that these corrections indeed restore the radiometric balance for each of the affected bands and substantially reduce the striping noise in the processed images.
Terra (T) MODerate-resolution Imaging Spectroradiometer (MODIS), a heritage Earth observing sensor has completed 15 years of operation as of December 18 2014. T-MODIS has 36 spectral channels designed to monitor the land, ocean, and atmosphere. The long term climate data record from T-MODIS is an important dataset for global change monitoring. Sixteen of the spectral channels fall in the Mid (M) (3.7-4.5μm) to Long (L) (6.7-14.1μm)Wave InfraRed (M/LWIR) wavelengths, which are also referred to as the Thermal Emissive Bands (TEBs). To date the TEBs have very satisfactory performance which is attributed to the scan-by-scan calibration using an on-board BlackBody whose temperature is traceable to the NIST temperature standards. However, with an aging instrument, it was observed from 2010 onwards that the Photo Voltaic LWIR channels (Bands 27-30) have suffered significantly from electronic crosstalk. This is mainly due to the deterioration of the electronic circuits of the relevant bands in the LWIR Focal Plane Array (FPA). In this paper, we report the characterization of the electronic crosstalk in the above-mentioned bands using the well characterized test site such as Dome Concordia (C). Such characterization can be used to reduce the effects of crosstalk when implemented in the future Level 1B reprocessing and thereby increasing the radiometric fidelity of the concerned bands.
Radiometric calibration is important for continuity and reliability of any optical sensor data. The Moderate Resolution Imaging Spectroradiometer (MODIS) onboard NASA EOS (Earth Observing System) Aqua satellite has been nominally operating since its launch on May 4, 2002. The MODIS thermal emissive bands (TEB) are calibrated using a quadratic calibration algorithm and the dominant gain term is determined every scan by reference to a temperature-controlled blackbody (BB) with known emissivity. On a quarterly basis, a BB warm-up and cool-down (WUCD) process is scheduled to provide measurements to determine the offset and nonlinear coefficients used in the TEB calibration algorithm. For Aqua MODIS, the offset and nonlinear terms are based on the results from prelaunch thermal vacuum tests. However, on-orbit trending results show that they have small but noticeable drifts. To maintain data quality and consistency, an iterative approach is applied to adjust the prelaunch based nonlinear terms, which are currently used to produce Aqua MODIS Collection-6 L1B. This paper provides details on how to use an iterative solution to determine these calibration coefficients based on BB WUCD measurements. Validation is performed using simultaneous nadir overpasses (SNO) of Aqua MODIS and the Infrared Atmospheric Sounding Interferometer (IASI) onboard the Metop-A satellite and near surface temperature measurements at Dome C on the Antarctic Plateau.
The MODerate-resolution Imaging Spectroradiometer (MODIS) is one of the primary instruments in the National Aeronautics and Space Administration (NASA) Earth Observing System (EOS). The first MODIS instrument was launched in December 1999 on-board the Terra spacecraft. MODIS has 36 bands, among which 27-30 are Long Wave Infrared (LWIR) PhotoVoltaic (PV) bands covering a wavelength range from 6.72 μm to 9.73 μm. It has been found that there is severe contamination in Terra band 27 from other three bands due to crosstalk of signals among them. The crosstalk effect induces strong striping in the Earth View (EV) images and causes large long-term drift in the EV Brightness Temperature (BT) in the band. An algorithm using a linear approximation derived from on-orbit lunar observations has been developed to correct the crosstalk effect for band 27. It was demonstrated that the crosstalk correction can substantially reduce the striping in the EV images and significantly remove the long-term drift in the EV BT. In this paper, it is shown that other three LWIR PV bands are also contaminated by the crosstalk of signals among themselves. The effect induces strong striping artifacts and large long-term drifts in these bands as similarly observed in band 27. The crosstalk correction algorithm previously developed is applied to correct the crosstalk effect. It is demonstrated that the crosstalk correction successfully reduces the striping in the EV images and removes long-term drifts in the EV BT in bands 28-30 as was done similarly for band 27. The crosstalk correction algorithm can thus substantially improve both the image quality and radiometric accuracy of the LWIR PV bands Level 1B (L1B) products. The algorithm can be applied to other MODIS bands and/or other remote sensors that exhibit an electronic crosstalk effect.
The first MODerate-resolution Imaging Spectroradiometer (MODIS), also known as the Proto-Flight model (PFM), is on-board the Terra spacecraft and has completed 14 years of on orbit flight as of December 18, 2013. MODIS remotely senses the Earth in 36 spectral bands, with a wavelength range from 0.4 μm to 14.4 μm. The 36 bands can be subdivided into two groups based on their spectral responsivity as Reflective Solar Bands (RSBs) and Thermal Emissive Bands (TEBs). Band 27 centered at 6.77 μm is a TEB used to study the global water vapor distribution. It was found recently that this band has been severely affected by electronic crosstalk. The electronic crosstalk magnitude, its on-orbit change and calibration impact have been well characterized in our previous studies through the use of regularly scheduled lunar observations. Further, the crosstalk correction was implemented in Earth view (EV) images and quantified the improvements of the same. However, improvements remained desirable on several fronts. Firstly, the effectiveness of the correction needed to be analyzed spatially and radiometrically over a number of scenes. Also, the temporal aspect of the correction had to be investigated in a rigorous manner. In order to address these issues, a one-orbit analysis was performed on the Level 1A (L1A) scene granules over a ten year period from 2003 through 2012. Results have been quantified statistically and show a significant reduction of image striping, as well as removal of leaked signal features from the neighboring bands. Statistical analysis was performed by analyzing histograms of the one-orbit granules at a scene and detector level before and after correction. The comprehensive analysis and results reported in this paper will be very helpful to the scientific community in understanding the impacts of crosstalk correction on various scenes and could potentially be applied for future improvements of band 27 calibration and, therefore, its retrieval for the Level 2 (L2) geophysical parameters.
Since launch in December 1999, Terra MODIS has successfully operated for nearly 15 years, making continuous observations. Data products derived from MODIS observations have significantly contributed to a wide range of studies of key geophysical parameters of the earth’s eco-system of land, ocean, and atmosphere, and their changes over time. The quality of MODIS data products relies on the dedicated effort to monitor and sustain instrument health and operation, to calibrate and update sensor parameters and properties, and to improve calibration algorithms. MODIS observations are made in 36 spectral bands, covering wavelengths from visible to long-wave infrared. The reflective solar bands (1-19 and 26) are primarily calibrated by a solar diffuser (SD) panel and regularly scheduled lunar observations. The thermal emissive bands (20-25 and 27- 36) calibration is referenced to an on-board blackbody (BB) source. On-orbit changes in the sensor spectral and spatial characteristics are monitored by a spectroradiometric calibration assembly (SRCA). This paper provides an overview of Terra MODIS on-orbit operation and calibration activities and implementation strategies. It presents and summarizes sensor on-orbit performance using nearly 15 years of data from its telemetry, on-board calibrators, and lunar observations. Also discussed in this paper are changes in sensor characteristics, corrections applied to maintain MODIS level 1B (L1B) data quality, and efforts for future improvements.
Terra and Aqua MODIS have operated near-continuously for over 14 and 12 years, respectively, and are key instruments for NASA’s Earth Observing System. Observations from the 16 thermal emissive bands (TEB), covering wavelengths from 3.5 to 14.4 μm with a nadir spatial resolution of 1 km are used to regularly generate a variety of atmosphere, ocean and land science products. The TEB detectors are calibrated using scan-by-scan observations of an on-board blackbody (BB). The current response versus scan angle (RVS) of the scan mirror was derived using a spacecraft deep-space pitch maneuver for Terra MODIS and characterized during prelaunch for Aqua MODIS. Earth view (EV) data over the complete range of angles of incidence (AOI) can be used to evaluate the on-orbit performance of the TEB RVS over the mission lifetime. Three approaches for tracking the TEB RVS on-orbit using EV observations are formulated. The first approach uses the multiple daily observations of Dome C BT at different AOI and their trend relative to coincident measurements from a ground temperature sensor. The second approach uses brightness temperatures (BT) retrieved over the cloud-free ocean to derive the trends at 13 AOI over the mission lifetime. The third approach tracks the dn response (normalized to the BB AOI) across the full swath width for Antarctic granules with the Dome C site at nadir. The viability of the three approaches is assessed and the long-term stability of the TEB RVS for both MODIS instruments is determined.
Since launch, Terra MODIS has successfully operated for more than 13 years and Aqua MODIS more than 11 years.
High quality science data products are continuously produced from sensor calibrated radiance and reflectance, or the
Level 1 (L1B) data products, and distributed to worldwide users for a broad range of studies of the earth’s land, ocean,
and atmospheric properties and their changes over time. MODIS observations are made in 20 reflective solar bands
(RSB) and 16 thermal emissive bands (TEB). The RSB are calibrated using data collected from its on-board solar
diffuser and lunar observations, and the TEB are calibrated by an on-board blackbody (BB). On-orbit changes in the
sensor’s spectral and spatial characteristics are monitored by an on-board spectroradiometric calibration assembly
(SRCA). This paper presents an overview of both Terra and Aqua MODIS on-orbit operations, calibration activities, and
methodologies applied from launch to present, and the current instrument status. It provides a summary of their
radiometric, spectral, and spatial calibration and characterization performance. It discusses on-orbit changes in sensor
characteristics and correction strategies applied to maintain the sensor calibration and level 1B (L1B) data quality,
including lessons that could benefit future calibration efforts and other earth-observing sensors.
The MODIS thermal emissive bands (TEB) are radiometrically calibrated on-orbit on a scan-by-scan basis, with reference to an aboard blackbody operated at 290 K for Terra MODIS and at 285 K for Aqua MODIS. The quality of the calibration can be evaluated with independent thermal sources at other temperatures. As a spectrally, spatially and radiometrically stable source, the Moon has become more important to the on-orbit calibration of space-borne spectral sensors that have regular lunar observation capability. MODIS is scheduled to observe the Moon on a nearly monthly basis at approximately the same lunar phase angle through its space view port. In this paper, the long-term stability of MODIS TEB radiometric calibration is assessed through the multi-year trends of the brightness temperatures (BT) of the lunar surface retrieved from the scheduled lunar observation. The highest lunar surface temperature is approximately 390 K, higher than the saturation temperatures of most TEB. For the non-saturated bands, the trending is based on the BT of the hottest area of the Moon. For the partially saturated bands, the trending is based on the BT difference of the unsaturated matching pixels between the band and a non-saturated reference band, given the fact that all MODIS bands are spatially registered. Overall, the trends have been stable throughout MODIS lifetime. The results also prove that the Moon can be used as a source to monitor the stability of the thermal bands.
The Terra and Aqua MODIS instruments have operated continuously for over 12 and 10 years respectively and are key contributors to the NASA Earth Observing System mission. The calibration for the 16 thermal emissive bands (TEB) is maintained on-orbit through scan-by-scan observations of a temperature controlled blackbody and deep space. Recently a potential calibration issue with Terra Band 29 (8.55 μm) was identified resulting in a possible long-term drift in Band 29 detector response. The long-term performance of Band 31 (11 μm) is considered stable and is used as a reference to track the relative stability of other TEB. Multiple observations of different Earth targets with a range of scene temperatures as a function of time are analyzed to assess MODIS TEB band-to-band calibration stability for Band 29.
The moderate-resolution imaging spectroradiometer (MODIS) was launched on the Terra spacecraft on Dec.18, 1999 and on Aquaon May 4, 2002. The data acquired by these instruments have contributed to the long-term climate data record for more than a decade and represent a key component of NASA’s Earth observing system. Each MODIS instrument observes nearly the whole Earth each day, enabling the scientific characterization of the land, ocean, and atmosphere. The MODIS Level 1B (L1B) algorithms input uncalibrated geo-located observations and convert instrument response into calibrated reflectance and radiance, which are used to generate science data products. The instrument characterization needed to run the L1B code is currently implemented using time-dependent lookup tables. The MODIS characterization support team, working closely with the MODIS Science Team, has improved the product quality with each data reprocessing. We provide an overview of the new L1B algorithm release, designated collection 6. Recent improvements made as a consequence of on-orbit calibration, on-orbit analyses, and operational considerations are described. Instrument performance and the expected impact of L1B changes on the collection 6 L1B products are discussed.
Since launch in May 2002, Aqua MODIS has successfully operated for over 10 years, continuously collecting global datasets for scientific studies of key parameters of the earth’s land, ocean, and atmospheric properties and their changes over time. The quality of these geophysical parameters relies on the input quality of sensor calibrated radiances. MODIS observations are made in 36 spectral bands with wavelengths ranging from visible (VIS) to long-wave infrared (LWIR). Its reflective solar bands (RSB) are calibrated using data collected from its on-board solar diffuser and regularly scheduled lunar views. The thermal emissive bands (TEB) are calibrated using an on-board blackbody (BB). The changes in the sensor’s spectral and spatial characteristics are monitored by an on-board spectroradiometric calibration assembly (SRCA). This paper presents an overview of Aqua MODIS 10-year on-orbit operation and calibration activities, from launch to present, and summarizes its on-orbit radiometric, spectral, and spatial calibration and characterization performance. In addition, on-orbit changes in sensor characteristics and corrections applied to continuously maintain level 1B (L1B) data quality are discussed, as well as lessons learned that could benefit future calibration efforts.
MODIS has 16 thermal emissive bands (TEB) with wavelengths ranging from 3.7 to 14.4 μm. MODIS TEB are calibrated on-orbit by a v-grooved blackbody (BB) on a scan-by-scan basis. The BB temperatures are measured by a set of 12 thermistors. As expected, the BB temperature uncertainty and stability have direct impact on TEB calibration quality and, therefore, the quality of the science products derived from TEB observations. Since launch, Terra and Aqua ODIS have successfully operated for more than 12 and 10 years, respectively. Overall performance of each on-board BB has been satisfactory, meeting the TEB on-orbit calibration requirements. The first VIIRS instrument was launched on-board the Suomi NPP spacecraft on October 28, 2011. It has successfully completed its initial Intensive Calibration and Validation (ICV) phase. As a followed-up instrument to MODIS, VIIRS has 7 TEB, covering wavelengths from 3.7 to 12.0 μm. Designed with strong MODIS heritage, VIIRS uses a similar BB for its TEB calibration. Like MODIS, VIIRS BB is nominally controlled at a constant temperature. Periodically, a BB Warm-Up and Cool-Down (WUCD) operation is performed, during which the BB temperatures vary from instrument ambient (temperature) to 315 K. Following a brief review of MODIS and VIIRS BB operation strategy, this paper examines and compares their on-orbit performance in terms of BB temperature scan-to-scan variations during sensor nominal operations as well as during periodic BB WUCD operations. In addition, this paper shows the noise characterization results for the closely matched MODIS and VIIRS spectral bands.
Terra and Aqua MODIS have operated continuously for more than 12 and 10 years respectively and are key instruments
for NASA’s Earth Observing System missions. The 16 thermal emissive bands (TEB), covering wavelengths from 3.5 to
14.4 μm with a nadir spatial resolution of 1 km are used to regularly generate a variety of atmosphere, ocean and land
science products. As the sensors age well past their prime design life of 6 years, understanding the instrument on-orbit performance is necessary to maintain consistency between sensors in the long-term data records. Recurrent observations of Dome C, Antarctica by both Terra and Aqua MODIS over mission lifetime are used to track the calibration consistency and stability of the two sensors. A ground temperature sensor provides a proxy reference measurement useful for determining the relative bias between the two instruments. This technique is most useful for the land surface sensing bands, such as bands 29, 31 and 32, but can be applied to all other TEB to provide a metric to assess long-term trends. A change in the TEB calibration approach for the MODIS Collection 6 reprocessing mitigate a cold scene bias previously observed for retrievals of brightness temperatures well below the on-board blackbody calibrator temperature range (270-315 K). The impact of the Collection 6 calibration changes are illustrated using the Dome C observations.
The MODerate Resolution Imaging Spectroradiometer (MODIS) is a heritage sensor operating on both the Terra and
Aqua platforms, and has collected remotely sensed data for a combined mission time of twenty plus years. The
instrument robustness and performance over their lifetimes has been very satisfactory and is well calibrated using the onboard
calibrators (OBC). The radiometric fidelity of the MODIS instruments has ensured the high quality of science
products derived from the Level 1B (L1B) imagery. MODIS Thermal Emissive Bands (TEB) are calibrated on-orbit
using an on-board blackbody (BB) and through the space-view (SV) port. The MODIS BB is nominally controlled at
290K for Terra and at 285K for Aqua. Periodically, a BB warm-up and cool-down (WUCD) process is implemented,
during which the BB temperatures vary from instrument ambient (approximately 272K) to 315K. The calibration
coefficients for the 16 TEB bands are characterized using the above mentioned on-board BB operations (i.e. using
nominal and WUCD operations). This paper will focus on the calibration algorithms of the TEB developed for collection
6 (C6) processing, its impact on the Level 1B (L1B) product in comparison to collection 5 (C5), and the methodology
for issuing a Look Up Table (LUT) update for L1B processing.
The MODIS instrument on the Terra and Aqua spacecrafts is a 12 bit sensor with an analog-to-digital (A/D) range of 0 to 4095 DN. Each sensor system is limited by a range at the low and high ends of the dynamic scale. At the low end, quantization noise is the limiting factor whereas at the high end the maximum value is limited by the capability
of the amplifier, 4095 in the case of MODIS. However, in both Terra and Aqua MODIS certain detectors in the Reflective Solar Bands (RSB) tend to pre-saturate at a value lower than 4095. This paper serves as a comprehensive report on the algorithms developed to characterize the pre-saturation limit in the RSB. The paper also provides the digital and pre-saturation (analog saturation) limits for the RSB that are currently being used in the Level 1B (L1B) products. The digital and analog saturation limits are well characterized using the Level 1A (L1A) raw Earth-View (EV) data and through the on-board Electronic Calibration (E-CAL). Also, in this paper an analysis is done to study
the sensors dynamic range due to the long term changes in the instrument response. In summary, the algorithms and results reported in this paper are important as the radiometric accuracy / uncertainty for instruments such as MODIS, VIIRS (NPP) tends to be coupled to pre-saturation.
The MODIS instruments on-board the Terra and Aqua spacecrafts have 16 thermal emissive bands (TEB), located on
two cold focal plane assemblies (CFPA). The CFPAs are cryogenically cooled by a passive radiative cooler, with their
temperatures further controlled at a nominal value of 83K. For Aqua MODIS, the cooler margin has gradually decreased
since launch, which deteriorates the CFPA temperature stability. Since 2006, Aqua CFPA temperature fluctuates with
the instrument temperature in both seasonal and orbital oscillation patterns. The magnitude of the fluctuation steadily
increases on yearly basis. The gains of TEB detectors change with the CFPA temperature in a nearly linear way, as is
demonstrated by both pre-launch calibration and on-orbit monitoring. As of mid 2012, the magnitude of the CFPA
temperature fluctuation reaches 0.65K, causing band-dependent detector gain fluctuation of up to 6%. In this paper, the
CFPA temperature and its related telemetries are monitored over both a short-term and long-term basis. The impact of
the fluctuation to TEB radiometric calibration is assessed, too. Because the calibration is normally performed on a scanby-
scan basis based on the observation of an onboard blackbody (BB), the detector gain change can be retrieved in
nearly real time. Therefore, the impact is insignificant in general. However, for bands 33, 35 and 36, their detectors
saturate when observing BB at BB temperature above certain saturation limits during quarterly held BB warmupcooldown
(WUCD) activities. Since there is no valid scan-by-scan calibration during these periods, a special treatment
has to be applied to calibrate these bands to reflect the detector gain fluctuation.
MODIS-Terra is one of the key sensors in the suite of remote sensing instruments in the Earth Observing System
(EOS). MODIS on the Terra platform was launched into orbit in December of 1999 and has successfully completed
eleven plus years of operation. MODIS has 36 spectral channels with wavelengths varying from 0.4 μm to 14.4 μm.
The native spatial resolutions for the reflective channels are 2 bands at 0.25 km, 5 bands at 0.5 km and 29 bands at
1km. However, the MODIS L1B product allows the high spatial resolution bands to be aggregated into 1km
resolution. All the thermal channels in MODIS (i.e. 3.75μm - 14.24μm) have a native spatial resolution of 1 km.
Over the eleven plus years of mission lifetime, the sensor degradation has been carefully monitored using various
On-Board Calibrators (OBC). In particular, the thermal channels are monitored using the on-board Black-Body (BB)
which is traceable to NIST standards. MODIS also has a unique feature for calibration reference in terms of lunar
irradiance. The lunar observations are scheduled for MODIS periodically (at least 9 observations in a calendar year).
Based on the lunar observations, it was found that there was a possible signal leak for band 27 from its neighboring
bands located on the Long-Wave Infrared (LWIR) focal plane. Further investigations revealed a possible leak from
bands 28, 29 and 30. The magnitude of the leak was trended and correction coefficients were derived. In this paper,
we demonstrate the across-band signal leak in MODIS band 27, its potential impact on the retrieved Brightness
temperature (B.T.). Also, the paper explores a correction methodology to relieve the artifacts due to the across-band
signal leak. Finally, the improvement in the band 27 image quality is quantified.
Launched in May 2002, the NASA EOS Aqua MODIS has successfully operated for more than 8 years. Observations
from Aqua MODIS and its predecessor, Terra MODIS, have generated an unprecedented amount of data products and
made significant contributions to studies of changes in the Earth's system of land, oceans, and atmosphere. MODIS
collects data in 36 spectral bands: 20 reflective solar bands (RSB) and 16 thermal emissive bands (TEB). It has a set of
on-board calibrators (OBC), providing sensor on-orbit radiometric, spectral, and spatial calibration and characterization.
This paper briefly summarizes Aqua MODIS on-orbit operation and calibration activities and illustrates instrument onorbit
performance from launch to present. Discussions are focused on OBC functions and changes in detector
radiometric gains, spectral responses, and spatial registrations. With ongoing calibration effort, Aqua MODIS will
continue serving the science community with high quality data products.
MODIS thermal emissive bands (TEB) are calibrated on-orbit via its on-board blackbody (BB) and observations
through its space view (SV) port. For Terra MODIS, the BB temperature is nominally controlled at 290K. Periodically,
a BB warm-up and cool-down (WUCD) process is scheduled and executed, during which the BB temperatures vary
from approximately 272K, the instrument ambient temperature, to 315K. The on-board BB temperatures are monitored,
on a scan-by-scan basis, using a set of 12 thermistors uniformly embedded in the BB panel. These thermistors were
characterized pre-launch and are traceable to the NIST temperature standards. Using more than 10 years of on-orbit
measurements, this paper reports Terra MODIS BB performance in terms of its temperature uniformity and stability.
On-orbit characterization is made when the BB is operated under the same or different configurations and conditions. In
this study, the variations of BB temperatures from its 12 individual thermistors are analyzed scan-by-scan in order to
assess its short-term stability and uniformity. To illustrate the long-term stability over the entire mission, only the
granule averaged BB temperatures are used. Results from this study will provide useful information for future missions
and sensors, such as NPP VIIRS and LDCM TIRS, in support of their on-board BB design, operation, and performance
The Moderate Resolution Imaging Spectroradiometer (MODIS) has been operating on both the Terra and Aqua
spacecraft for over 10.5 and 8 years, respectively. Over 40 science products are generated routinely from MODIS Earth
images and used extensively by the global science community for a wide variety of land, ocean, and atmosphere
applications. Over the mission lifetime, several versions of the MODIS data set have been in use as the calibration and
data processing algorithms evolved. Currently Version 5 MODIS data is the baseline Level-1B calibrated science
product. The MODIS Characterization Support Team (MCST), with input from the MODIS Science Team, developed
and delivered a number of improvements and enhancements to the calibration algorithms, Level-1B processing code and
Look-up Tables for the Version 6 Level-1B MODIS data. Version 6 implements a number of changes in the calibration
methodology for both the Reflective Solar Bands (RSB) and Thermal Emissive Bands (TEB). This paper describes the
improvements introduced in Collection 6 to the RSB and TEB calibration and detector Quality Assurance (QA)