CERES Flight Model 6 and Radiation Budget Instrument (RBI) Status

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First-Principle Dynamic Electro-Thermal Numerical Model of a Scanning Radiometer for Earth Radiation Budget Applications

Low Earth Observing instruments that are used to monitor the incoming solar and outgoing long wave radiation have been a crucial part of studying the Earths radiation budget for the past three decades. These instruments go through several robust design phases followed by vigorous ground calibration campaigns to set their baseline characterization spectrally, spatially, temporally and radiometrically. The knowledge from building and calibrating these instruments has aided in technology advancements and the need for developing more accurate instruments has increased. In order to understand the on-ground instrument performance, NASA Langley Research Center has partnered with the Thermal Radiation Group of Virginia Tech to develop a first-principle, dynamic, electrothermal, numerical model of a scanning radiometer that can be used to enhance the interpretation of an Earth radiation budget-like instrument on orbit. This paper will summarize the current efforts of developing this high-fidelity end-to-end model and also highlight how it can be applied to an Earth radiation budget instrument

Future Flight Opportunities and Calibration Protocols for CERES: Continuation of Observations in Support of the Long-Term Earth Radiation Budget Climate Data Record

The goal of the Clouds and the Earth s Radiant Energy System (CERES) project is to provide a long-term record of radiation budget at the top-of-atmosphere (TOA), within the atmosphere, and at the surface with consistent cloud and aerosol properties at climate accuracy. CERES consists of an integrated instrument-algorithm validation science team that provides development of higher-level products (Levels 1-3) and investigations. It involves a high level of data fusion, merging inputs from 25 unique input data sources to produce 18 CERES data products. Over 90% of the CERES data product volume involves two or more instruments. 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 . Five CERES instruments have flown on three different spacecraft: TRMM, EOS-Terra and EOS-Aqua. In response, NASA, NOAA and NPOESS have agreed to fly the existing CERES Flight Model (FM-5) on the NPP spacecraft in 2011 and to procure an additional CERES Sensor with modest upgrades for flight on the JPSS C1 spacecraft in 2014, followed by a CERES follow-on sensor for flight in 2018. CERES is a scanning broadband radiometer that measures filtered radiance in the SW (0.3-5 m), total (TOT) (0.3-200 m) and WN (8-12 m) regions. Pre-launch calibration is performed on each Flight Model to meet accuracy requirements of 1% for SW and 0.5% for outgoing LW observations. Ground to flight or in-flight changes are monitored using protocols employing onboard and vicarious calibration sources. Studies of flight data show that SW response can change dramatically due to optical contamination. with greatest impact in blue-to UV radiance, where tungsten lamps are largely devoid of output. While science goals remain unchanged for ERB Climate Data Record, it is now understood that achieving these goals is more difficult for two reasons. The first is an increased understanding of the dynamics of the Earth/atmosphere system which demonstrates that separation of natural variability from anthropogenic change on decadal time scales requires observations with higher accuracy and stabili

Using Lunar Observations to Validate Pointing Accuracy and Geolocation, Detector Sensitivity Stability and Static Point Response of the CERES Instruments

Validation of in-orbit instrument performance is a function of stability in both instrument and calibration source. This paper describes a method using lunar observations scanning near full moon by the Clouds and Earth Radiant Energy System (CERES) instruments. The Moon offers an external source whose signal variance is predictable and non-degrading. From 2006 to present, these in-orbit observations have become standardized and compiled for the Flight Models -1 and -2 aboard the Terra satellite, for Flight Models-3 and -4 aboard the Aqua satellite, and beginning 2012, for Flight Model-5 aboard Suomi-NPP. Instrument performance measurements studied are detector sensitivity stability, pointing accuracy and static detector point response function. This validation method also shows trends per CERES data channel of 0.8% per decade or less for Flight Models 1-4. Using instrument gimbal data and computed lunar position, the pointing error of each detector telescope, the accuracy and consistency of the alignment between the detectors can be determined. The maximum pointing error was 0.2 Deg. in azimuth and 0.17 Deg. in elevation which corresponds to an error in geolocation near nadir of 2.09 km. With the exception of one detector, all instruments were found to have consistent detector alignment from 2006 to present. All alignment error was within 0.1o with most detector telescopes showing a consistent alignment offset of less than 0.02 Deg

Coloration Determination of Spectral Darkening Occurring on a Broadband Earth Observing Radiometer: Application to Clouds and the Earth's Radiant Energy System (CERES)

It is estimated that in order to best detect real changes in the Earth s climate system, space based instrumentation measuring the Earth Radiation Budget (ERB) must remain calibrated with a stability of 0.3% per decade. Such stability is beyond the specified accuracy of existing ERB programs such as the Clouds and the Earth s Radiant Energy System (CERES, using three broadband radiometric scanning channels: the shortwave 0.3 - 5microns, total 0.3. > 100microns, and window 8 - 12microns). It has been shown that when in low earth orbit, optical response to blue/UV radiance can be reduced significantly due to UV hardened contaminants deposited on the surface of the optics. Since typical onboard calibration lamps do not emit sufficient energy in the blue/UV region, this darkening is not directly measurable using standard internal calibration techniques. This paper describes a study using a model of contaminant deposition and darkening, in conjunction with in-flight vicarious calibration techniques, to derive the spectral shape of darkening to which a broadband instrument is subjected. Ultimately the model uses the reflectivity of Deep Convective Clouds as a stability metric. The results of the model when applied to the CERES instruments on board the EOS Terra satellite are shown. Given comprehensive validation of the model, these results will allow the CERES spectral responses to be updated accordingly prior to any forthcoming data release in an attempt to reach the optimum stability target that the climate community requires

Enhancing the Ground Calibration in the Short-wavelength Region to Improve Traceability within the Reflected Solar Bands of the CERES Instrument

The Clouds and Earth’s Radiation Energy System (CERES) program produces data of solar-reflected and earth-emitted radiation from the top-of-atmosphere (TOA), within the atmosphere, and at the Earth’s surface. This program currently employs six instruments onboard four different spacecraft to measure and produce long-term record of the earth’s energy budget. CERES Flight Model 6 (FM6), the instrument that will fly on the Joint Polar Satellite System (JPSS) -1 spacecraft, is a scanning broadband radiometer consisting of three sensors that measure three different spectral radiances: solar region consisting of wavelength between 0.3 to 5 microns, total region between 0.3 to 200 microns, and a broadband region of 5 to 40 microns. Rigorous pre-launch ground calibration is performed on these sensors to meet accuracy requirements of 1% and 0.5% for shortwave and longwave radiance observations, respectively. A Cryogenically cooled Transfer Active Cavity Radiometer (TACR), one of the components of the pre-launch ground calibration facility, was modified in efforts to improve traceability within the reflected solar bands (shortwave and total channels). These modifications included replacing the heritage mirrors from enhanced silver coating to protected aluminum, which in turn resulted in a greater signal-to-noise ratio. These findings along with efforts to quantify the spectral response of the new TACR’s optics from UV to IR are discussed in this paper

Optimization of Thickness Allocation Between Two Fused Silica Filters

A recurring challenge in bandpass thermal radiation measurement applications requiring a high degree of accuracy is the treatment of secondary radiation emitted from the filter itself. Considered is the important case of the short-wavelength channels implemented in CERES, RBI, and most other Earth radiation budget instruments. In these applications broadband radiation incident between 0.2 and 100 μm traverses a low-pass filter whose cut-off wavelength is around 5 μm. The filter material of choice is fused silica, which filters by absorption. Ideally most of the heat absorbed beyond 5 μm is conducted to the filter mount so that the filter temperature remains essentially constant during a scan cycle. In practice, however, the filter temperature must vary to some extent, resulting in time-varying emission from both faces. Because of the relatively low temperature of the filter, around 300 K, its peak emission occurs at around 10 μm. Radiation emitted from the face nearest the detector inevitably leads to a phase-delayed time-varying noise component that adds to and is indistinguishable from the radiation passed by the filter. A common solution to this problem is to introduce a second filter in series with the primary filter which intercepts and absorbs the emitted noise component, as shown in the figure. Because space in the optical stack-up is often limited, it is desirable to optimally distribute the total available space between the two filters; i.e. to determine the optimum value of the ratio t2/(t1 + t2). A process is reported for accomplishing this based on a hybrid thermal diffusion/ray-trace model

Production of a Multi-decadal Earth Radiation Budget Climate Data Record: Balancing Accuracy, Precision, and Data Availability to Meet the Needs of the Community

NASA’s Earth Radiation Budget Science Team, ERB-ST, (Previously known as the CERES Science Team) is a multi-disciplinary team led out of NASA’s Langley Research Center which has the responsibility for governance of the nation’s multi-decadal Earth Radiation Budget Climate Data Record, ERB CDR. The Science Data Processing System which produces the ERB-CDR is highly complex, producing Level one through Level 4 products. The system ingests data from 19 different instruments on 11 different spacecraft (6 GEO and 5 LEO) as well as other ancillary information, producing 25 different products with consistent TOA, Surface, and atmospheric radiative fluxes, cloud and aerosol properties on multiple spatial and temporal scales. Spatial scales vary from instantaneous/pixel (25 km), 1-deg grid, zonal, regional and global means while temporal scales vary across instantaneous, hourly, 3 hourly to monthly scales. Accuracy and precision values vary across the various spatial and temporal scales, with the long-term goal of measuring decadal trends of better than 0.3 W/m^2 per decade. Instrument calibration and precision, as measured through the post-launch protocols, is one of many considerations that drive the decision to reprocess, others include, but are not limited to validation and instantiation of new algorithms across all levels of products, outside teams reprocessing the products we ingest, the launch of new instrumentation to replace operational weather imagers on Geo satellites, updates to processing hardware, and of course resource availability. These all need to be managed/considered in order to provide the global community products of sufficient accuracy and precision on a time-scale which allows continued advancement and discovery of key scientific questions such that policy makers may make informed decisions. This presentation will highlight the process the Earth Radiation Budget Science Team currently utilizes to guide reprocessing decisions, identifying lessons learned and best practices