B. Guenther

Development, characterization, and performance of the EOS MODIS sensors

The MODerate-resolution Imaging Spectroradiometer (MODIS) is the keystone instrument for the NASA’s Earth Observing System (EOS). Currently two nearly identical MODIS instruments are operating on-board the EOS Terra spacecraft (launched in December 1999) and the EOS Aqua spacecraft (launched in May 2002), providing global coverage of the Earth’s land, oceans, and atmosphere with both morning and afternoon observations. This paper reviews the EOS MODIS development history, its design concepts, system implementation and calibration, current status and the follow-on Visible/Infrared Imaging Radiometer Suite (VIIRS) under development for the National Polar Orbiting Environmental Satellite System (NPOESS).

On-orbit characterization of a solar diffuser’s bidirectional reflectance factor using spacecraft maneuvers

The MODerate Resolution Imaging Spectroradiometer (MODIS) uses an on-board solar diffuser (SD) panel made of Spectralon for the radiometric calibration of its 20 reflective solar bands (RSB). The spectral wavelengths of the RSB range from 0.41 to 2.1 micrometers. The on-orbit calibration coefficients are determined from the sensor s responses to the diffusely reflected solar illumination from the SD. This method requires an accurate pre-launch characterization of solar diffuser s bi-directional reflectance factors (BRF) that should cover the sensor s spectral range and illumination/viewing angles and accurate on-orbit monitoring of SD degradation over time. The MODIS SD panel s bi-directional reflectance factors were characterized prior to the sensor s final system integration (pre-launch by the instrument vendor using reference samples traceable to the NIST reflectance standards at a number of wavelengths and carefully selected combinations of the illumination/viewing angles. The measured BRF values were fitted into smooth surfaces and then interpolated for each of the MODIS reflective solar bands. In this paper, we describe an approach designed for the MODIS on-orbit characterization and validation of its SD BRF using multiple SD solar observations at several spacecraft yaw angels. This approach has been successfully applied to both the Terra and Aqua MODIS. This paper presents the algorithm used to derive the SD s relative BRF from observations during spacecraft yaws and compares the on-orbit results with corresponding pre-launch values.

Lessons learned from MODIS

Abstract The Moderate Resolution Imaging Spectroradiometer (MODIS) was launched onboard the Earth Observing System (EOS) Terra spacecraft on December 18, 1999 and onboard the Aqua spacecraft on May 4, 2002. This paper examines the MODIS performance during more than three years of on-orbit operation together with data from fifteen years of pre-launch development and testing for possible improvements in design choices, practices and procedures that may prove useful in the development of future space-borne multi-spectral radiometers. Topics considered include onboard calibration, scattered light, electrical and optical cross talk, and scan mirror performance.

VIIRS on-orbit optical anomaly: investigation, analysis, root cause determination and lessons learned

A gradual, but persistent, decrease in the optical throughput was detected during the early commissioning phase for the Suomi National Polar-Orbiting Partnership (SNPP) Visible Infrared Imager Radiometer Suite (VIIRS) Near Infrared (NIR) bands. Its initial rate and unknown cause were coincidently coupled with a decrease in sensitivity in the same spectral wavelength of the Solar Diffuser Stability Monitor (SDSM) raising concerns about contamination or the possibility of a system-level satellite problem. An anomaly team was formed to investigate and provide recommendations before commissioning could resume. With few hard facts in hand, there was much speculation about possible causes and consequences of the degradation. Two different causes were determined as will be explained in this paper. This paper will describe the build and test history of VIIRS, why there were no indicators, even with hindsight, of an on-orbit problem, the appearance of the on-orbit anomaly, the initial work attempting to understand and determine the cause, the discovery of the root cause and what Test-As-You-Fly (TAYF) activities, can be done in the future to greatly reduce the likelihood of similar optical anomalies. These TAYF activities are captured in the “lessons learned” section of this paper.

On-orbit Characterization of RVS for MODIS Thermal Emissive Bands

Response versus scan angle (RVS) is a key calibration parameter for remote sensing radiometers that make observations using a scanning optical system, such as a doubled sided scan mirror (MODIS and GLI) or a rotating telescope (SeaWiFS and VIIRS). This is because the calibration is typically performed at a fixed viewing angle whereas the Earth scene observations are made over a range of viewing angles and the system’s response is a function of the scan angle. The NASA EOS Terra MODIS has been in operation for more than four years since its launch in December 1999. It has 36 spectral bands covering wavelengths from visible (VIS) to long-wave infrared (LWIR). It is a cross-track scanning radiometer with a two-sided paddle wheel scan mirror, making observations over a wide field of view (FOV) of ±55° from nadir thereby enabling frequent global coverage. Due to pre-launch measurement limitations, the Terra MODIS thermal emissive bands (TEB) RVS characterization did not produce valid data sets that could be used to derive a reliable system level RVS. Because of this, a RVS was developed for use at launch and subsequent efforts have been made to characterize the RVS using on-orbit observations. This paper describes the Terra MODIS on-orbit characterization of TEB RVS, including the data from scanning the instrument’s closed nadir aperture door (CNAD) and the use of Earth view data collected during spacecraft deep space maneuvers (DSM). Comparisons of pre-launch analysis and early on-orbit measurements are also provided. Noticeable improvements have been made for several thermal emissive bands for observations at large angles of incidence (AOI). Using the correct RVS improves the image quality and the radiometric calibration accuracy. For bands 34-36, an adjustment of as much as 0.5-1.5K can be made at the end of scan (worst case) for mirror side 2. The impacts at smaller AOI and from mirror side 1 are much smaller. Based on RVS comparison studies and science test results, the on-orbit derived DSM RVS has been chosen for the ongoing L1B data processing and future reprocessing.

MODIS Level 1B calibration and data products

The Moderate Resolution Imaging Spectroradiometer (MODIS) is an Earth-viewing sensor that is currently operating on the EOS-Terra and EOS-Aqua satellites. Each MODIS instrument has 36 bands. Data are received from 490 detectors in these reflective Solar and infrared emissive bands. Calibration of the 490 channels on each MODIS instrument is performed by the MODIS Characterization Support Team (MCST), which works closely with the members of the MODIS Science Team to provide a calibration product that is useful for their geophysical products. The MODIS Level 1B (L1B) algorithm performs radiometric calibration for the duration of each mission. The L1B input files, output data products, and the emissive and reflective calibration algorithms are described. The Look-up Tables (LUTs) that provide the instrument characterization needed to run the L1B software are also described. We briefly present the L1B code standards, properties, and enhancement process. Lastly, lessons learned are discussed.

Modeling SNPP VIIRS reflective solar bands optical throughput degradation and its impacts on the relative spectral response

Right after the opening of the NADIR door of the Visible/Infrared Imager/Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership (SNPP) satellite, it has been observed that the detector gains of the near infrared (NIR) bands have decreased much faster than expected. This large decrease is attributed to the optical reflectance degradation of the Rotating Telescope Assembly (RTA) mirrors. We have established a physical model to describe the degradation. In this Proceeding, we use the model to fit the up-to-date observed data to update the model parameters’ values and the degradation projections. We have adjusted our original model slightly to address the additional optical throughput degradation for the short wave infrared (SWIR) bands, occurred right after the spacecraft Sun Point mode anomaly (orbits 2101-2133; March 24-26, 2012). The RTA optical throughput degradation over the reflective solar bands (RSB) and the additional throughput degradation over the SWIR bands after the Sun Point mode anomaly are not constant across the optical wavelength and therefore impact on a detector’s relative spectral response (RSR). Using the models, we establish the degradation versus wavelength curve at any orbit and use the curve to compute the associated impact on the RSR. We further use this degradation modulated RSR to compute the impact on sensor calibration and the Earth View reflectance at Sensor Data Record (SDR) level.

Results and lessons from MODIS thermal emissive bands calibration : Pre-launch to on-orbit

The Moderate Resolution Imaging Spectroradiometer (MODIS) is a major instrument for NASAs Earth Observing System (EOS), currently operating on-board the EOS Terra spacecraft, launched in December 1999, and Aqua spacecraft, launched in May 2002. MODIS is a whiskbroom scanning radiometer using a double-sided paddle wheel scan mirror. It makes measurements in 36 spectral bands with wavelengths from visible (VIS) to long-wave infrared (LWIR). Bands 20-25 and 27-36 are the thermal emissive bands (TEB) covering wavelengths from 3.5 to 14.4μm. During pre-launch thermal vacuum measurements, a laboratory blackbody calibration source (BCS) was used as the primary calibration source for the TEB. For on-orbit operation, an on-board blackbody (BB) source and a space view (SV) port are used together for the TEB calibration on a scan-by-scan basis. This paper provides an overview of Terra and Aqua MODIS pre-launch and on-orbit calibration and characterization activities, methodologies, data analysis results, and lessons learned for the thermal emissive bands. It focuses on major issues that could impact MODIS TEB calibration and data quality. Results presented in this paper include detector noise characterization, response versus scan angle (RVS), and response versus instrument and focal plane temperatures. Similar discussions for the MODIS reflective solar bands (RSB) are presented in a separate paper in these proceedings (Xiong et. al).

Results and Lessons from MODIS Reflective Solar Bands Calibration: Pre-launch to On-orbit

MODIS is a major instrument for NASAs EOS missions, currently operating aboard the EOS Terra and Aqua spacecraft launched in December 1999 and May 2002, respectively. It was designed to extend heritage sensor measurements and data records and to enable new research studies of the Earths land, oceans, and atmosphere. MODIS has 36 spectral bands (0.41 - 14.4μm) located on four focal plane assemblies (FPA). It makes measurements at three nadir spatial resolutions: 0.25km, 0.5km, and 1km. Because of instrument design complexity and more stringent calibration requirements, extensive calibration and characterization activities were conducted pre-launch by the sensor vendor for both Terra and Aqua MODIS. For the 20 reflective solar bands (RSB) with wavelengths below 2.2μm, these activities include detector noise characterization, radiometric response at different instrument temperatures and at different scan angles, and relative spectral response. On-orbit RSB calibration is performed using a solar diffuser (SD) and a solar diffuser stability monitor (SDSM). In addition, regular lunar observations are made to track RSB radiometric stability. This paper provides a summary of Terra and Aqua MODIS RSB pre-launch and on-orbit calibration and characterization activities, methodologies, data analysis results, and lessons learned. It focuses on major issues that could impact MODIS RSB calibration and data product quality. Results presented in this paper include RSB detector noise characterization, response versus scan angle and instrument temperature, SD bi-directional reflectance factors characterization, and on orbit calibration stability. Similar discussions on MODIS thermal emissive bands (TEB) are presented in a separate paper in these proceedings (Xiong et. al).

MODIS radiometric calibration program, methods and results

As a key instrument for NASAs Earth Observing System (EOS), the Moderate Resolution Imaging Spectroradiometer (MODIS) has made significant contributions to the remote sensing community with its unprecedented amount of data products continuously generated from its observations and freely distributed to users worldwide. MODIS observations, covering spectral regions from visible (VIS) to long-wave infrared (LWIR), have enabled a broad range of research activities and applications for studies of the earths interactive system of land, oceans, and atmosphere. In addition to extensive pre-launch measurements, developed to characterize sensor performance, MODIS carries a set of on-board calibrators (OBC) that can be used to track on-orbit changes of various sensor characteristics. Most importantly, dedicated and continuous calibration efforts have been made to maintain sensor data quality. This paper provides an overview of the MODIS calibration program, on-orbit calibration activities, methods, and performance. Key calibration results and lessons learned from the MODIS calibration effort are also presented in this paper.