Phillip C. Hess

Radiometric Performance of the CERES Earth Radiation Budget Climate Record Sensors on the EOS Aqua and Terra Spacecraft through April 2007

Abstract The Clouds and the Earth’s Radiant Energy System (CERES) flight models 1 through 4 instruments were launched aboard NASA’s Earth Observing System (EOS) Terra and Aqua spacecraft into 705-km sun-synchronous orbits with 10:30 p.m. and 1:30 a.m. local time equatorial crossing times. With these instruments CERES provides state-of-the-art observations and products related to the earth’s radiation budget at the top of the atmosphere (TOA). The archived CERES science data products consist of geolocated and calibrated instantaneous filtered and unfiltered radiances through temporally and spatially averaged TOA, surface, and atmospheric fluxes. CERES-filtered radiance measurements cover three spectral bands: shortwave (0.3–5 μm), total (0.3>100 μm), and an atmospheric window channel (8–12 μm). CERES climate data products realize a factor of 2–4 improvement in calibration accuracy and stability over the previotus Earth Radiation Budget Experiment (ERBE) products. To achieve this improvement there are three...

Validation of Geolocation of Measurements of the Clouds and the Earth’s Radiant Energy System (CERES) Scanning Radiometers aboard Three Spacecraft

Abstract The Clouds and the Earth’s Radiant Energy System (CERES) instrument is a scanning radiometer for measuring Earth-emitted and -reflected solar radiation to understand Earth’s energy balance. One CERES instrument was placed into orbit aboard the Tropical Rainfall Measuring Mission (TRMM) in 1997; two were aboard the Terra spacecraft, launched in 1999; and two were aboard the Aqua spacecraft, launched in 2002. These measurements are used together with data from higher-resolution instruments to generate a number of data products. The nominal footprint size of the pixel at Earth’s surface is 16 km in the cross-scan direction and 23 km in the scan direction for the TRMM platform and 36 km in the cross-scan direction and 46 km in the scan direction for the Terra and Aqua platforms. It is required that the location on Earth of each pixel be known to 1–2 km to use the CERES data with the higher-resolution instruments on a pixel basis. A technique has been developed to validate the computed geolocation of ...

Performance assessment of the Clouds and the Earth's Radiant Energy System (CERES) instruments aboard Terra and Aqua spacecraft

Clouds and the Earths Radiant Energy System (CERES) instruments were designed to measure the reflected shortwave and emitted longwave radiances of the Earth’s radiation budget and to investigate the cloud interactions with global radiances for the long-term monitoring of Earths climate. The three scanning thermistor bolometer sensors on CERES measure broadband radiances in the shortwave (0.3 to 5.0 micrometer), total (0.3 to <100 micrometer) and in 8 - 12 micrometer water vapor window regions. Of the five CERES instruments that are currently in operation, four of the CERES instruments (Flight Models1 through 4) fly aboard Earth Observing System (EOS) Terra and Aqua platforms with two instruments aboard each spacecraft, in 705 KM sun-synchronous orbits of 10:30 AM and 1:30 PM equatorial crossing time. A rigorous and comprehensive radiometric calibration and validation protocol comprising of various studies was developed to evaluate the calibration accuracy of the CERES instruments. The in-flight calibration of CERES sensors are carried out using the internal calibration module (ICM) comprising of blackbody sources and quartzhalogen tungsten lamp, and a solar diffuser plate known as the Mirror Attenuator Mosaic (MAM). The ICM calibration results are instrumental in determining the changes in CERES sensors’ gains after launch from the prelaunch determined values and the on-orbit gain variations. In addition to the broadband response changes derived from the on-board blackbody and the tungsten lamp, the shortwave and the total sensors show a spectrally dependent drop in responsivity in the shorter wavelegth region below one micron that were brought to light through validation studies. The spectrally dependent changes were attributed to the instrument operational modes and the corrections were derived using the sensor radiance comparisons. This paper covers the on-orbit behavior of CERES sensors aboard the Terra and Aqua spacecraft and the determination of the sensor response changes utilising the in-flight calibration and the radiance measurement comparisons viewing various targets. The corrections for the sensor response changes were incorporated in the radiance calculations of CERES Edition3 data products.

NPP clouds and the Earth's Radiant Energy System (CERES) predicted sensor performance calibration and preliminary data product performance

Continuation of the Earth Radiation Budget (ERB) Climate Data Record (CDR) has been identified as critical in the 2007 NRC Decadal Survey, the Global Climate Observing System WCRP report, and in an assessment titled ‘Impacts of NPOESS Nunn-McCurdy Certification on Joint NASA-NOAA Climate Goals’. In response, the final existing CERES Flight Model (FM-5) will fly on the NPP spacecraft for launch in 2010. The CERES FM-5 pre-flight radiometric characterization program has benefited from the operational experience of the CERES EOS sensors. Improvements to the pre-flight program included increased sampling under vacuum conditions and additional tests to characterize the primary and transfer standards in the calibration facility. Future opportunities for ERB CDR continuity consist of procuring an additional CERES Sensor with modest performance upgrades for flight on the NPOESS C1 spacecraft in 2013, followed by a new CERES follow-on sensor for flight in 2018 on the NPOESS C3 spacecraft.

Geolocation validation of CERES instruments using radiance measurements

Clouds and the Earths Radiant Energy System (CERES) instruments are currently flying on two satellite platforms, Terra, launched 18 December 1999 and Aqua, launched 04 May 2002. Both satellites are at a 705-km altitude, in high inclination, polar orbits. Terra crosses the equator at local morning, while Aqua crosses at local afternoon. Each platform carries two CERES instruments. Each CERES instrument contains three scanning radiation-detecting bolometers. The three detectors measure reflected solar and Earth emitted radiation in three bandwidths: shortwave (0.3-5 μm), window (8-12 μm), and total (0.3 to >100 μm). Earth views of each instrument are geolocated to the Earth fixed coordinate system using satellite attitude, ephemeris, and instrument pointing data. An analysis has been developed which uses radiation gradients at ocean-land boundaries measured by the CERES instrument as an aid to validate the computed geolocation. The detected coastlines are compared to known map coordinates and an error analysis is performed after a best fit is made in the coastline comparison. Spatial differences are mapped from latitude, longitude to absolute distance in along-track (ground path) and cross-track (perpendicular to ground path) of the satellite. Results of the Terra CERES instruments have shown maximum errors to be within 10% of the nadir footprint size. A description of the coastline detection and error analysis will be presented along with results for the Terra CERES instruments. Initial results from the coastline detection and error analysis for the Aqua instruments will be presented also.

Assessment of the clouds and the Earth’s Radiant Energy System (CERES) instrument performance and stability on the Aqua, Terra, and S-NPP spacecraft

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.

Assessment of the Clouds and the Earth’s Radiant Energy System (CERES) Flight Model 5 (FM5) instrument performance and stability

The Clouds and the Earth’s Radiant Energy System (CERES) scanning radiometer is designed to measure the solar radiation reflected by the Earth and thermal radiation emitted by the Earth. Four CERES instruments are supporting the EOS missions; two aboard the Terra spacecraft, launched in 1999 and two aboard the Aqua spacecraft, launched in 2002. A fifth instrument, Flight Model 5 (FM5), launched in October 2011 aboard the S-NPP satellite, began taking radiance measurements on January 27th, 2012. The CERES FM5 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 assess the pointing accuracy of the instrument and understand any spectral changes that may occur with the sensors allowing for corrections to be made to the radiance calculations in later CERES data products. This paper summarizes the on-orbit behavior of the CERES FM5 instrument by outlining trends in the internal calibration data and discussing the various validation studies used to assess the performance and stability of the instrument.

Early trends on the CERES FM5 instrument performance using in-flight calibration sources

The Clouds and the Earth’s Radiant Energy System (CERES) scanning radiometer is designed to measure the solar radiation reflected by the earth and thermal radiation emitted by the earth. Four CERES instruments are already in service; two aboard the Terra spacecraft, launched in 1999; and two aboard the Aqua spacecraft, launched in 2002. A fifth instrument, flight model 5 (FM5), launched in October 2011 aboard the NPP satellite, began taking radiance measurements on January 27th, 2012. The CERES FM5 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 calibration sources are used to define shifts or drifts in the sensor response over the life of the mission. In order to better understand the sensors adaptation to the space environment, daily internal calibrations were conducted on all three channels for the first week after opening the instrument’s main covers. Over the next month, the frequency of internal calibrations was reduced to the standard mission schedule of three total and window channel calibrations per week and one shortwave channel calibration per week. This paper presents the results of FM5 on-orbit internal calibrations, discusses any ground to flight changes, and describes trends in the calibration data.

On-orbit solar calibration methods using the Clouds and Earth's Radiant Energy System (CERES) in-flight calibration system: lessons learned

The Clouds and Earths Radiant Energy System (CERES) scanning thermistor bolometers measure earth-reflected solar and earth-emitted long-wave radiances, at the top- of-the-atmosphere. The bolometers measure the earth radiances in the broadband shortwave solar (0.3-5.0 microns) and total (0.3->100 microns) spectral bands as well as in the 8->12 microns water vapor window spectral band over geographical footprints as small as 10 kilometers at nadir. December 1999, the second and third set of CERES bolometers was launched on the Earth Observing Mission Terra Spacecraft. May 2003, the fourth and fifth set of bolometers was launched on the Earth Observing Mission Aqua Spacecraft. Recently, (October 2011) the sixth instrument was launched on the National Polar-orbiting Operational Environmental Satellite System Preparatory Project (Suomi NPP) Spacecraft. Ground vacuum calibrations define the initial count conversion coefficients that are used to convert the bolometer output voltages into filtered earth radiances. The mirror attenuator mosaic (MAM), a solar diffuser plate, was built into the CERES instrument package calibration system in order to define on-orbit shifts or drifts in the sensor responses. It followed a similar design as the Earth Radiation Budget Experiment (ERBE) scanners with improvements from lessons learned. The shortwave and shortwave part of the total-wave sensors are calibrated using the solar radiances reflected from the MAMs. Each MAM consists of baffle-solar diffuser plate systems, which guide incoming solar radiances into the instrument fields of view of the shortwave and total wave sensor units. The MAM diffuser reflecting type surface consists of an array of spherical aluminum mirror segments, which are separated by a Merck Black A absorbing surface, over-coated with SIOx (SIO2 for PFM). Thermistors are located within each MAM plate and the total channel baffle. The CERES MAM is designed to yield calibration precisions approaching .5 percent for the total and shortwave detectors. The Terra FM1 and FM2 shortwave channels and the FM1 and FM2 total channels MAM calibration systems showed shifts in their solar calibrations of 1.5, 2.5, 1.5 and 6 percent, respectively within the first year. The Aqua FM3, and FM4 shortwave channels and the FM3 and FM4 total channels MAM calibration systems showed shifts in their solar calibrations of 1.0, 1.2, 2.1 and .8 percent, respectively within the first year. A possible explanation has attributed the MAM reflectance change to on-orbit solar ultraviolet/atomic oxygen/out-gassing induced chemical changes to the SIOx coated MAM assembly during ram and solar exposure. There is also changes to the sensor telescope shortwave filters as well as the Total channel mirrors and/or sensors. The Soumi NPP FM5 is still after 2.5 years displaying a stability of less than .5 percent. In this presentation, lessons learned from the ERBE MAM and application of knowledge of how the space environment affected the CERES FM1-4 solar calibrations will be presented along with on-orbit measurements for the thirteen years the CERES instruments have been on-orbit.

A strategy to assess the pointing accuracy of the CERES (FM5) scanner

The Clouds and the Earth’s Radiant Energy System (CERES) scanning radiometer is designed to measure the solar radiation reflected by the Earth and thermal radiation emitted by the Earth. Four CERES instruments are already in service; two aboard the Terra spacecraft, launched in 1999; and two aboard the Aqua spacecraft, launched in 2002. A fifth instrument (FM5), launched in October 2011 aboard the NPP satellite, began taking radiance measurements in January 2012. A technique to validate the computed geolocation of CERES measurements is referred to as a coastline detection algorithm. This technique relies on a rapid gradient change of measurements taken over a well-defined and known Earth target, such as a coastline, where a strong contrast in brightness and temperature exists. The computed coastline is then compared with World Bank II map to verify the accuracy of the measurement location. Our goal is to process the first five months of CERES FM5 data for a preliminary assessment of the pointing accuracy of the FM5 scanner. The paper briefly restates the algorithm used in the study, describes collection of coastline data, and shows results of error in a pixel geolocation in the direction of a scan (XT) and also along the groundtrack of the satellite (AT).