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Dr. Mohan Shankar

Dr. Mohan ShankarMohan Shankar is the CERES Deputy Project Scientist who supports the CERES Project Scientist and IWG chair, responsible for (1) the development and implementation of calibration and validation protocols and delivery of all ancillary data to ensure timely availability of Level-1 data products, and (2) monitoring the health and operations of all currently operational CERES instruments.

The Instrument Working Group (IWG) is responsible for monitoring the instrument health, instrument operations, developing instrument calibration and validation protocols and executing them, as well as providing all necessary ancillary data to ensure the availability of Level-0 and Level-1 data products. The responsibilities of this team start before launch and continues throughout the life of the mission. The IWG works closely with the instrument vendor during the instrument build and performance characterization, participates in performance verification prior to, during and after spacecraft integration and is responsible for post-launch checkout followed by mission operations. The team also schedules and executes specific ground or field campaigns as requested by members of the science team.

Contact Information

NASA Langley Research Center
Mail Stop 420, Hampton, VA 23681-2199

Phone: 757-864-2507

Fax: 757-864-7996





Shankar, Mohan; Loeb, Norman G.; Smith, Nathaniel; Smith, Natividad; Daniels, Janet L.; Thomas, Susan; Walikainen, DaleShankar, M., N. G. Loeb, N. Smith, N. Smith, J. L. Daniels, S. Thomas, D. Walikainen, 2023: Evaluating the Radiometric Performance of the Clouds and the Earth’s Radiant Energy System (CERES) Instruments on Terra and Aqua Over 20 Years. IEEE Transactions on Geoscience and Remote Sensing, 61, 1-11. doi: 10.1109/TGRS.2023.3330398. Six Clouds and the Earth’s Radiant Energy System (CERES) instruments on four satellites are used to produce a global continuous multidecadal record of Earth’s radiation budget (ERB) at the top-of-atmosphere (TOA). Each CERES instrument was calibrated and characterized on the ground before launch, while postlaunch calibration was conducted using onboard calibration sources. The performance of the CERES instruments is verified using vicarious approaches involving both Earth and celestial targets. In this article, we describe the calibration and validation approach and demonstrate the performance of the CERES instruments on the Terra and Aqua spacecraft over the 20-year period since launch. Validation results demonstrate that after applying the appropriate calibration corrections, all four instruments are stable and perform consistently with each other. Comparisons of observations between instruments on the two spacecraft during orbital crossings further confirm the consistent performance across all instruments over the 20-year period. validation; Earth; Clouds and the Earth’s Radiant Energy System (CERES); calibration; Calibration; radiometry; Radiometry; Aqua; Terra; Space vehicles; Mirrors; Optical filters; Telescopes


Shankar, Mohan; Su, Wenying; Manalo-Smith, Natividad; Loeb, Norman G.Shankar, M., W. Su, N. Manalo-Smith, N. G. Loeb, 2020: Generation of a Seamless Earth Radiation Budget Climate Data Record: A New Methodology for Placing Overlapping Satellite Instruments on the Same Radiometric Scale. Remote Sensing, 12(17), 2787. doi: 10.3390/rs12172787. The Clouds and the Earth’s Radiant Energy System (CERES) instruments have enabled the generation of a multi-decadal Earth radiation budget (ERB) climate data record (CDR) at the top of the Earth’s atmosphere, within the atmosphere, and at the Earth’s surface. Six CERES instruments have been launched over the course of twenty years, starting in 1999. To seamlessly continue the data record into the future, there is a need to radiometrically scale observations from newly launched instruments to observations from the existing data record. In this work, we describe a methodology to place the CERES Flight Model (FM) 5 instrument on the Suomi National Polar-orbiting Partnership (SNPP) spacecraft on the same radiometric scale as the FM3 instrument on the Aqua spacecraft. We determine the required magnitude of radiometric scaling by using spatially and temporally matched observations from these two instruments and describe the process to radiometrically scale SNPP/FM5 to Aqua/FM3 through the instrument spectral response functions. We also present validation results after application of this radiometric scaling and demonstrate the long-term consistency of the SNPP/FM5 record in comparison with the CERES instruments on Aqua and Terra. calibration; radiation budget; radiometric scaling


Smith, Natividad; Thomas, Susan; Shankar, Mohan; Priestley, Kory; Loeb, Norman; Walikainen, DaleSmith, N., S. Thomas, M. Shankar, K. Priestley, N. Loeb, D. Walikainen, 2018: Assessment of on-orbit variations of the Clouds and the Earth's Radiant Energy System (CERES) FM5 instrument. Earth Observing Missions and Sensors: Development, Implementation, and Characterization V, 10781, 1078119. doi: 10.1117/12.2324739. The Clouds and the Earth’s Radiant Energy System (CERES) mission is instrumental in monitoring changes in the Earth’s radiant energy and cloud systems. The CERES project is critical in guaranteeing the continuation of highly accurate Earth radiation budget Climate Data Records (CDRs). The CERES Flight Model-5 (FM-5) instrument, integrated onto the Suomi-National Polar-Orbiting Partnership (NPP) spacecraft, joined a suite of four CERES instruments deployed aboard NASA’s Earth Observing System (EOS) satellites Terra and Aqua. Each CERES instrument consists of scanning thermistor bolometer sensors that measure broadband radiances in the shortwave (0.3 to 5μm), total (0.3 to < 200 μm) and water vapor window (8 to 12 μm) regions. In order to ensure the consistency and accuracy of instrument radiances, needed for generating higher-level climate data products, the CERES project implements rigorous and comprehensive radiometric calibration and validation procedures. This paper briefly describes the trends observed in Edition-1 FM5 flux data products that are corrected for inflight gain changes derived from on-board calibration sources. The strategy to detect artifacts and correct for any sensor spectral response changes is discussed. Improvements and validation results of preliminary FM5 Edition-2 products will be compared with Terra and Aqua data products.


Loeb, Norman G.; Manalo-Smith, Natividad; Su, Wenying; Shankar, Mohan; Thomas, SusanLoeb, N. G., N. Manalo-Smith, W. Su, M. Shankar, S. Thomas, 2016: CERES Top-of-Atmosphere Earth Radiation Budget Climate Data Record: Accounting for in-Orbit Changes in Instrument Calibration. Remote Sensing, 8(3), 182. doi: 10.3390/rs8030182. The Clouds and the Earth’s Radiant Energy System (CERES) project provides observations of Earth’s radiation budget using measurements from CERES instruments onboard the Terra, Aqua and Suomi National Polar-orbiting Partnership (S-NPP) satellites. As the objective is to create a long-term climate data record, it is necessary to periodically reprocess the data in order to incorporate the latest calibration changes and algorithm improvements. Here, we focus on the improvements and validation of CERES Terra and Aqua radiances in Edition 4, which are used to generate higher-level climate data products. Onboard sources indicate that the total (TOT) channel response to longwave (LW) radiation has increased relative to the start of the missions by 0.4% to 1%. In the shortwave (SW), the sensor response change ranges from −0.4% to 0.6%. To account for in-orbit changes in SW spectral response function (SRF), direct nadir radiance comparisons between instrument pairs on the same satellite are made and an improved wavelength dependent degradation model is used to adjust the SRF of the instrument operating in a rotating azimuth plane scan mode. After applying SRF corrections independently to CERES Terra and Aqua, monthly variations amongst these instruments are highly correlated and the standard deviation in the difference of monthly anomalies is 0.2 Wm−2 for ocean and 0.3 Wm−2 for land/desert. Additionally, trends in CERES Terra and Aqua monthly anomalies are consistent to 0.21 Wm−2 per decade for ocean and 0.31 Wm−2 per decade for land/desert. In the LW, adjustments to the TOT channel SRF are made to ensure that removal of the contribution from the SW portion of the TOT channel with SW channel radiance measurements during daytime is consistent throughout the mission. Accordingly, anomalies in day–night LW difference in Edition 4 are more consistent compared to Edition 3, particularly for the Aqua land/desert case. calibration; earth radiation budget; Satellite; climate; Radiance


Shankar, Mohan; Priestley, Kory; Smith, Nathaniel; Smith, Nitchie; Thomas, Susan; Walikainen, DaleShankar, M., K. Priestley, N. Smith, N. Smith, S. Thomas, D. Walikainen, 2015: Radiometric calibration and performance trends of the Clouds and Earth’s Radiant Energy System (CERES) instruments onboard the Terra and Aqua spacecraft. Proc. SPIE 9639, Sensors, Systems, and Next-Generation Satellites XIX, 9639, 963915-963915-13. doi: 10.1117/12.2194468. The Clouds and Earth’s Radiant Energy System (CERES) instruments help to study the impact of clouds on the earth's radiation budget. There are currently five instruments- two each on board Aqua and Terra spacecraft and one on the Suomi NPP spacecraft to measure the earth’s reflected shortwave and emitted longwave energy, which represent two components of the earth’s radiation energy budget. Flight Models (FM) 1 and 2 are on Terra, FM 3 and 4 are on Aqua, and FM5 is on Suomi NPP. The measurements are made by three sensors on each instrument: a shortwave sensor that measures the 0.3-5 microns wavelength band, a window sensor that measures the water vapor window between 8-12 microns, and a total sensor that measures all incident energy (0.3- >100 microns). The required accuracy of CERES measurements of 0.5% in the longwave and 1% in the shortwave is achieved through an extensive pre-launch ground calibration campaign as well as on-orbit calibration and validation activities. Onorbit calibration is carried out using the Internal Calibration Module (ICM) that consists of a tungsten lamp, blackbodies, and a solar diffuser known as the Mirror Attenuator Mosaic (MAM). The ICM calibration provides information about the stability of the sensors’ broadband radiometric gains on-orbit. Several validation studies are conducted in order to monitor the behavior of the instruments in various spectral bands. The CERES Edition-4 data products for the FM1-FM4 instruments incorporate the latest calibration methodologies to improve on the Edition-3 data products. In this paper, we discuss the updated calibration methodology and present some validation studies to demonstrate the improvement in the trends using the CERES Edition-4 data products for all four instruments.
Smith, Nathaniel P.; Thomas, Susan; Shankar, Mohan; Hess, Phillip C.; Smith, Natividad M.; Walikainen, Dale R.; Wilson, Robert S.; Priestley, Kory J.Smith, N. P., S. Thomas, M. Shankar, P. C. Hess, N. M. Smith, D. R. Walikainen, R. S. Wilson, K. J. Priestley, 2015: Assessment of the clouds and the Earth’s Radiant Energy System (CERES) instrument performance and stability on the Aqua, Terra, and S-NPP spacecraft. SPIE 9607, Earth Observing Systems XX, 9607, 96070T-96070T-10. doi: 10.1117/12.2190110. The Clouds and the Earth’s Radiant Energy System (CERES) scanning radiometer is designed to measure reflected solar radiation and thermal radiation emitted by the Earth. Five CERES instruments are currently taking active measurements in-orbit with two aboard the Terra spacecraft (FM1 and FM2), two aboard the Aqua spacecraft (FM3 and FM4), and one aboard the S-NPP spacecraft (FM5). The CERES instrument uses three scanning thermistor bolometers to make broadband radiance measurements in the shortwave (0.3 – 5.0 micrometers), total (0.3 - >100 micrometers) and water vapor window (8 – 12 micrometer) regions. An internal calibration module (ICM) used for in-flight calibration is built into the CERES instrument package consisting of an anodized aluminum blackbody source for calibrating the total and window sensors, and a shortwave internal calibration source (SWICS) for the shortwave sensor. The ICM sources, along with a solar diffusor called the Mirror Attenuator Mosaic (MAM), are used to define shifts or drifts in the sensor response over the life of the mission. In addition, validation studies are conducted to understand any spectral changes that may occur with the sensors and assess the pointing accuracy of the instrument, allowing for corrections to be made to the radiance calculations in CERES data products. This paper covers the observed trends in the internal and solar calibration data, discusses the latest techniques used to correct for sensor response, and explains the validation studies used to assess the performance and stability of the instrument.


Mohan Shankar, Nikos P. Pitsianis and David J. BradyMohan Shankar, Nikos P. Pitsianis and David J. Brady, 2010: Compressive video sensors using multichannel imagers. Applied Optics, 49(10). doi: 10.1364/AO.49.0000B9.


Mohan Shankar, Nikos P. Pitsianis and David J. BradyMohan Shankar, Nikos P. Pitsianis and David J. Brady, 2008: Spatio-temporal sampling for video. SPIE Proceedings, Image Reconstruction from Incomplete Data V, 7076. doi: 10.1117/12.795753.
Mohan Shankar, Rebecca Willett, Nikos Pitsianis, Timothy Schulz, Robert Gibbons, Robert Te Kolste, James Carriere, Caihua Chen, Dennis Prather and David Brady,Mohan Shankar, Rebecca Willett, Nikos Pitsianis, Timothy Schulz, Robert Gibbons, Robert Te Kolste, James Carriere, Caihua Chen, Dennis Prather and David Brady,, 2008: Thin Infrared Imaging Systems through Multi-Channel Sampling. Applied Optics, 47(10). doi: 10.1364/AO.47.0000B1.


Mohan Shankar, John Burchett, Qi Hao, Bob Guenther and David BradyMohan Shankar, John Burchett, Qi Hao, Bob Guenther and David Brady, 2006: Human-tracking systems using Pyroelectric infrared detectors. Optical Engineering, 45(10). doi: 10.1117/1.2360948.
Mohan Shankar, R. Willett, and N. P. Pitsianis, R. Te Kolste, C. Chen, R. Gibbons and D. BradyMohan Shankar, R. Willett, and N. P. Pitsianis, R. Te Kolste, C. Chen, R. Gibbons and D. Brady, 2006: Ultra-thin multiple channel LWIR Imaging Systems. SPIE Proceedings, Infrared and Photoelectronic Imagers and Detector Devices II, 6294. doi: 10.1117/12.681386.


Mohan Shankar, John Burchett, Steven D. Feller, Brandon Jones, Russell Swagart, Bob D. Guenther, and David J. BradyMohan Shankar, John Burchett, Steven D. Feller, Brandon Jones, Russell Swagart, Bob D. Guenther, and David J. Brady, 2005: Biometric tracking with coded pyroelectric sensor clusters. SPIE Proceedings, Unattended Ground Sensor Technologies and Applications VII, 5796. doi: 10.1117/12.606557.