With increased spectral, spatial, and temporal resolution, the Hyperspectral Environmental Suite (HES) of the Geostationary Operational Environmental Satellite (GOES)-R Series will contribute to a significant improvement in the GOES products, including an increase in the number of products over the current GOES Imager and Sounder, especially when combined with the GOES-R Advanced Baseline Imager (ABI). The planned capabilities of the HES are encompassed by tasks, which describe required performance for operating at required scan rates. The scheduling of the HES will be determined by NOAA (National Oceanic and Atmospheric Administration). A range of possible scan scenarios for optimizing the collection of data for users with a variety of geographic or phenomenological concerns will be discussed here. One such schedule from the sounding capability of the HES would be a full "sounding disk" at 10 km (sub-satellite point resolution) covered every three hours, as well as the contiguous U.S. every hour at 4 km resolution, plus selected other regions of interest. The HES Coastal Waters (CW) will provide coverage of the coastal areas every three hours, in addition to other regions such as the Great Lakes, or other features of interest.
The GOES satellites will fly a Hyperspectral Environmental Suite (HES) on GOES-R in the 2012 timeframe. The approximately 1500 spectral channels (technically ultraspectral), leading to improved vertical resolution, and approximately five times faster coverage rate planned for the sounder in this suite will greatly exceed the capabilities of the current GOES series instrument with its 18 spectral channels. In the GOES-R timeframe, frequent measurements afforded by geostationary orbits will be critical for numerical weather prediction models. Since the current GOES soundings are assimilated into numerical weather prediction models to improve the validity of model outputs, particularly in areas with little radiosonde coverage, this hyperspectral capability in the thermal infrared will significantly improve sounding performance for weather prediction in the western hemisphere, while providing and enhancing other products. Finer spatial resolution is planned for mesoscale observation of water vapor variations. The improvements over the previous GOES sounders and a primary difference from other planned instruments stem from two-dimensional focal plane array availability. These carry an additional set of challenges in terms of instrument specifications, which will be discussed. As a suite, HES is planned with new capabilities for coastal ocean coverage with the goal of including open ocean coverage. These new planned imaging applications, which will be either multispectral or hyperspectral, will also be discussed.
Remote sensing of the atmosphere and the surface of the earth is performed by the Imager and Sounder instruments onboard the GOES (Geostationary Operational Environmental Satellite) Satellites. By employing large PV Hg1CdTe focal plane array (FPA) detectors, instruments like the Advanced Baseline Imager (ABI) and Advanced Baseline Sounder (ABS) will provide improved update times, resolution, and sensitivity. However, uniformity in the pixel geometry across the array must first be demonstrated in order to maintain the accuracy of weather products at each spot on the ground. This uniformity is particularly important in weather products involving radiance subtractions and ratios from multiple spectral bands employing different detectors. Measurement ofthe spatial response associated with a pixel is important in determining both ground resolution and the effect ofradiance from outside the pixel field-of-view. Therefore, a high precision test set-up has been developed at Lincoln Laboratory to measure both the modulation transfer function (MTF) associated with each pixel in the array and the cross-talk from pixel to pixel. Details of the test set up and initial results of the testing will be discussed.
Remote sensing of the atmosphere and surface of the earth is performed by the Imager and Sounder instruments onboard the GOES (Geostationary Operational Environmental Satellite) Satellites. The current versions of these instruments have two and four detectors per band, respectively, that are scanned across the earth. Large photovoltaic, Hg1-xCdx Te Focal Plane Arrays (FPAs) will permit faster coverage, improved resolution, and improved sensitivity for future designs like the Advanced Baseline Imager (ABI) and the Advanced Baseline Sounder (ABS). However, the transition away from the current small number of detectors requires a technology demonstration of the same or better radiometric precision and uniformity across available FPAs. These measurements, using appropriate flux levels, f-numbers, and readout rates for GOES, are underway at MIT Lincoln Laboratory. Both corrected response from pixel to pixel (residual spatial non-uniformity) and temporal stability of each pixel during the calibration period are required to better than 0. 1 K NEdT. The test set-up and the measurements of dark current and signal performance will be discussed for two arrays.
The Emergency GOES Imager study responds to the potential need for a small, back-up imager for weather observations in the event of failure of one or more of the current GOES satellites. The Emergency GOES Imager (EGI) is designed to be compact and lightweight. Minimal spatial resolution is required in the visible and IR band for the purpose of synoptic forecasts. The ground resolution requirement is 16 km for the 10.2 to 11.2 micrometers IR band and 4 km for the 0.5 to 0.7 micrometers visible band. Due to the small size of the instrument, the EGI has the potential to be deployed either alone on a small launcher or as an auxiliary payload on a larger satellite. The overall size of the EGI is dependent on the orientation of the satellite because of the dependence on amount of solar shielding required for the cooler, and the choice of coolers for specific satellite orientations. Although the EGI design is for an emergency system, the design utilizes recent technology in the form of both a linear IR focal plane array, in front of its constant-motion mirror, and a visible CCD array with a staring-format. The IR array has the potential to present a technical challenge to array manufacturers in the area of calibration, assuming a 0.1 K NEDT. We discuss the means by which the emergency requirements are met with this small and simple system, define the limiting technologies in the design, and explore modifications necessary to expand these requirements.
A Fabry-Perot annular summing spectroscopy technique has been sued at the University of Wisconsin's Pine Bluff Observatory to acquire geocoronal Balmer-(alpha) line profile data with significantly improved precision and height resolution. The double-etalon Fabry-Perot interference pattern is imaged onto a photometrics PM512 CCD chip, thus enabling light to be gathered in multiple spectral bins simultaneously. In comparison with scanning systems we used earlier, the high quantum efficiency of the CCD and the multi-channel detection associated with the Fabry-Perot annular summing technique have enabled us to save a factor of about 10 in the integration time required for studies of the line profile. As a result, we are now able to both more precisely observe the line shape of the very faint Balmer- (alpha) emission and obtain data using shorter integration times. Our data illustrate the scientific potential for using this technique for the study of very faint extended emission line sources. The increase in the signal-to-noise of our data has enabled us to examine Balmer-(alpha) profile asymmetries which we have found to be compatible with predictions that on the order of 10 percent of the geocoronal Balmer-(alpha) excitation arises from cascades due to higher-member solar Lyman series excitation. This fine structure was overlooked in previous Balmer-(alpha) studies aimed at determining non-Maxwellian dynamical properties of exospheric hydrogen; we find that cascade excitation largely masks the expected very small dynamical perturbations to the line profile at low shadow heights, and must be more thoroughly studied before drawing conclusions about exospheric dynamics. Accounting for cascade laos leads to more realistic determinations of exospheric hydrogen temperatures near the exobase.
This paper describes Fabry-Perot/CCD annular summing applied to airglow observations. Criteria are developed for determining the optimal rectangular format CCD chip configuration which minimizes dark and read noise. The relative savings in integration time of the imaging Fabry-Perot/CCD system over the pressure-scanned Fabry-Perot/PMT system is estimated for the optimal configuration through calculations of the signal to noise ratios for three extreme (but typical) cases of source and background intensity. The largest savings in integration time is estimated for the daysky thermospheric [O<SUP>1</SUP>D] (6300 angstrom) case where the bright (approximately equals 5 X 10<SUP>6</SUP>R/A) Rayleigh-scattered background dominates the read noise. The long integration times required to obtain useful signal to noise ratios for the faint (approximately equals 10R) nightsky exospheric hydrogen Balmer-(alpha) (6563 angstrom) reduce the importance of the read noise term and yield large savings in integration time. The significance of the read noise term is greatly increased with the very short estimated integration times required for bright (approximately equals 200R) nightsky lines such as thermospheric [O<SUP>1</SUP>D]. Alternate CCD formats and applications methods that reduce read noise and provide improved performance in the latter case are compared against the CCD annular summing technique.