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43 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

MODIS On-Orbit Calibration and Lessons Learned

The Moderate Resolution Imaging Spectroradiometer (MODIS) is a key instrument for NASA's Earth Observing System (EOS) Terra and Aqua missions. Since launch, Terra and Aqua MODIS have successfully operated for more than 12 and 10 years, respectively, and generated an unprecedented amount of data products for the science and user community over a wide range of applications. MODIS was developed with improved design and stringent calibration requirements over its heritage sensors in order . to extend and enhance their long-term data records. Its follow-on instrument, the Visible/Infrared Imager Radiometer Suite (VIIRS), was launched on-board the Suomi National Polar-orbiting Partnership (NPP) spacecraft October 28, 2011. MODIS collects data in 36 spectral bands, covering wavelengths from 0.41 to 14.S!Jlll, and at 250m, SOOm, and lkm spatial resolutions (nadir). MODIS on-orbit calibration is provided by a set of onboard calibrators (OBC), including a solar diffuser (SO), a solar diffuser stability monitor (SDSM), a blackbody (BB), and a spectroradiometric calibration assembly (SRCA). In addition to the onboard calibrators, regular lunar observations are made by both Terra and Aqua MODIS to track their calibration stability in the reflective solar region. This tutorial session provides an overview of MODIS on-orbit calibration and characterization methodologies. It discusses challenging issues and lessons learned from sensor design, operation, calibration, and inter-comparisons. Examples of instrument on-orbit performance are illustrated with a focus on the improvements made based on various lessons learned. It is expected that MODIS experience and lessons will continue to provide valuable information for future earth observing missions/sensors.

Xiong, Jack↗
NASA NTRS2012

Overview of Aqua MODIS 10-year On-orbit Calibration and Performance

Since launch in May 2002, Aqua MODIS has successfully operated for nearly 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 longwave 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, it will illustrate and discuss on-orbit changes in sensor characteristics and corrections applied to continuously maintain the sensor level 1B (L1B) data quality, as well as lessons learned that could benefit future calibration efforts.

Xiong, X.↗
NASA NTRS2004

Status of Aqua MODIS On-orbit Calibration and Characterization

The MODIS Flight Model 1 (FM1) has been in operation for more than two years since its launch onboard the NASA's Earth Observing System (EOS) Aqua spacecraft on May 4, 2002. The MODIS has 36 spectral bands: 20 reflective solar bands (RSB) with center wavelengths from 0.41 to 2.2 micron and 16 thermal emissive bands (TEB) from 3.7 to 14.5 micron. It provides the science community observations (data products) of the Earth's land, oceans, and atmosphere for a board range of applications. Its primary on-orbit calibration and characterization activities are performed using a solar diffuser (SD) and a solar diffuser stability monitor (SDSM) system for the RSB and a blackbody for the TEB. Another on-board calibrator (OBC) known as the spectro-radiometric calibration assembly (SRCA) is used for the instrument's spatial (TEB and RSB) and spectral (RSB only) characterization. We present in this paper the status of Aqua MODIS calibration and characterization during its first two years of on-orbit operation. Discussions will be focused on the calibration activities executed on-orbit in order to maintain and enhance the instrument's performance and the quality of its Level 1B (L1B) data products. We also provide comparisons between Aqua MODIS and Terra MODIS (launched in December, 1999), including their similarity and difference in response trending and optics degradation. Existing data and results show that Aqua MODIS bands 8 (0.412 micron) and 9 (0.443 micron) have much smaller degradation than Terra MODIS bands 8 and 9. The most noticeable feature shown in the RSB trending is that the mirror side differences in Aqua MODIS are extremely small and stable (<0.1%) while the Terra MODIS RSB trending has shown significant mirror side difference and wavelength dependent degradation. The overall stability of the Aqua MODIS TEB is also better than that of the Terra MODIS during their first two years of on-orbit operation.

Aqua↗
NASA NTRS2014

Status of Terra MODIS Operation, Calibration, and Performance

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↗
NASA NTRS2018

Effects of Time-Varying Relative Spectral Response on the Calibration of MODIS Reflective Solar Bands

Calibration of the on-orbit gain changes of the narrow bandwidth reflective solar bands (RSB) of Terra and Aqua MODIS is usually based on the band center wavelength. The relative spectral response (RSR) of each band is assumed to be constant on orbit and the time dependence of an overall gain factor is calculated. Any on-orbit changes to the RSR of the MODIS bands will introduce some error into the calibration and may also have an impact on the Earth scene radiance retrieval. We consider two different ways to track how the RSR of the MODIS RSB may be changing on orbit, and the effect that these changes will have on the calibration. First, we examine in-band RSR measurements from the spectro-radiometric calibration assembly (SRCA) carried on-board both MODIS instruments. Second, we study the broadband degradation of the MODIS scan mirror and how it may be changing the effective out-of-band response of the RSB. We find that RSR changes have a small effect on the radiance calibrated using the on-board solar diffuser, generally less than 0.5% in all cases at any time in the missions, with bands 1, 8, and 9 impacted the most.

Twedt, Kevin A.↗
NASA NTRS2020

Effects of Out-of-Band and Time-Varying Relative Spectral Response on the Calibration of MODIS Reflective Solar Bands

Calibration of the on-orbit gain changes of the narrow bandwidth reflective solar bands (RSB) of Terra and Aqua MODIS is usually based on the band center wavelength. The relative spectral response (RSR) of each band is assumed to be constant on orbit and the time dependence of an overall gain factor is calculated. Any on-orbit changes to the RSR of the MODIS bands will introduce some error into the calibration and may also have an impact on the Earth scene radiance retrieval. We consider two different ways to track how the RSR of the MODIS RSB may be changing on orbit, and the effects that these changes will have on the calibration. First, we study the broadband degradation of the MODIS scan mirror and how it may be changing the effective out-of-band response of the RSB. Second, we examine in-band RSR measurements from the spectro-radiometric calibration assembly (SRCA) carried on-board both MODIS instruments. We find that RSR changes have a relatively small effect on the radiance calibrated using the on-board solar diffuser, generally less than 0.5% for all RSB at any time in the missions, though the effect may be slightly larger for some scan angles. The impact of RSR changes on the Earth scene radiance retrieval is highly dependent on the spectral properties of the scene and could be significantly larger. The bands showing the largest impacts are Terra bands 1, 4, 8, 9, 17, and 19 and Aqua bands 8 and 9.

MODIS↗
NASA NTRS2022

Surface Corrected Lunar MTF Measurements in MODIS and VIIRS Using the SP Model

Lunar observations have been used for sensor performance assessments for a number of Earth-observing instruments, including the Moderate Resolution Imaging Spectroradiometer (MODIS) on board Terra and Aqua and the Visible Infrared Imaging Radiometer Suite (VIIRS) on board Suomi-NPP (SNPP) and NOAA-20 (N20). While the primary purpose of lunar observations in MODIS and VIIRS is radiometric calibration, these observations have been leveraged for other sensor performance assessments such as spatial registration and deriving the modulation transfer function (MTF). In this work, we will derive the lunar MTF using a knife edge approach similar to previous work. However, to further isolate the edge of the lunar disk when deriving the edge spread function (ESF), we will apply a lunar surface variation correction using a model based on data obtained by the Spectral Profiler (SP) on board the SELENE spacecraft. This model was provided to us by AIST in Japan. To align the measured and modeled data, we developed techniques for projecting the measured lunar surface pixels onto the radiance maps produced by the SP model. We correct the lunar surface variation while preserving the signal of the lunar disk edge in the ESF, and then calculate the MTF results using standard techniques. These results are in good agreement with previously published results from both Moon-based observations in MODIS and VIIRS and from the spectroradiometric calibration assembly (SRCA) on MODIS. With the exception of MODIS bands 1 and 2, the MTF is stable on orbit for the reflective bands in both instruments.

MODIS↗