Dr. Graziela R. Keller Profile

Dr. Graziela R. Keller

Senior Research Scientist at Science Systems and Applications Inc

SPIE Involvement:

Author

Publications (6)

SPIE Journal Paper | 23 February 2018

GEO-LEO reflective band intercomparison with bidirectional reflectance distribution function and atmospheric scattering corrections

Tiejun Chang, Xiaoxiong Xiong, Graziela Keller, Xiangqian Wu

JARS, Vol. 12, Issue 01, 014002, (February 2018) https://doi.org/10.1117/12.10.1117/1.JRS.12.014002

KEYWORDS: Reflectivity, Bidirectional reflectance transmission function, Atmospheric corrections, Scattering, Sensors, Satellites, Calibration, Atmospheric modeling, Rayleigh scattering, Imaging systems

Read Abstract +

The intercomparison of the reflective solar bands (RSB) between the instruments onboard a geostationary orbit satellite and a low Earth orbit satellite is very helpful in assessing their calibration consistency. Himawari-8 was launched on October 7, 2014, and Geostationary Operational Environmental Satellite (GOES)-R was launched on November 19, 2016. Unlike previous GOES instruments, the Advanced Himawari Imager (AHI) on Himawari-8 and the Advanced Baseline Imager (ABI) on GOES-R have onboard calibrators for the RSB. Independent assessment of calibration is nonetheless important to enhance their product quality. MODIS and visible infrared imager radiometer suite (VIIRS) can provide good references for sensor calibration. The intercomparison between AHI and VIIRS is performed over a pseudoinvariant target. The use of stable and uniform calibration sites provides comparison with accurate adjustment for band spectral difference, reduction of impact from pixel mismatching, and consistency of BRDF and atmospheric correction. The site used is the Strzelecki Desert in Australia. Due to the difference in solar and view angles, two corrections must be applied to compare the measurements. The first is the atmospheric scattering correction applied to the top of atmosphere reflectance measurements. The second correction is applied to correct the BRDF effect. The atmospheric correction is performed using a vector version of the Second Simulation of a Satellite Signal in the Solar Spectrum (6SV) model and the BRDF correction is performed using a semiempirical model. Our results show that AHI band 1 (0.47 μm) has a good agreement with VIIRS band M3 within 0.15%. AHI band 5 (1.61 μm) shows the largest difference (5.09%) with VIIRS band M10, whereas AHI band 5 shows the least difference (1.87%) in comparison with VIIRS band I3. The methods developed in this work can also be directly applied to assess GOES-16/ABI calibration consistency, a topic we will address in the future.

Proceedings Article | 29 September 2017 Presentation + Paper

Aqua MODIS electronic crosstalk survey from Moon observations

Graziela Keller, Zhipeng Wang, Aisheng Wu, Xiaoxiong Xiong

Proceedings Volume 10423, 1042314 (2017) https://doi.org/10.1117/12.2277972

KEYWORDS: Sensors, Calibration, MODIS, Contamination, Image sensors, Reflectivity, Sensor calibration, Satellite imaging, Satellites, Scanners

Read Abstract +

Proceedings Article | 5 September 2017 Paper

MTF analysis using lunar observations for Himawari-8/AHI

Graziela Keller, Tiejun Chang, Xiaoxiong Xiong

Proceedings Volume 10402, 104022I (2017) https://doi.org/10.1117/12.2274091

KEYWORDS: Modulation transfer functions, Satellite imaging, Imaging systems, Calibration, Algorithm development, Remote sensing, Earth observing sensors

Read Abstract +

Proceedings Article | 5 September 2017 Paper

Bridging the thermal band comparison between LEO-LEO sensors and between GEO-GEO sensors

Tiejun Chang, Graziela Keller, Xiaoxiong (Jack) Xiong

Proceedings Volume 10402, 104022F (2017) https://doi.org/10.1117/12.2272794

KEYWORDS: MODIS, Sensors, Calibration

Read Abstract +

Proceedings Article | 5 September 2017 Presentation + Paper

GEO-LEO reflectance band inter-comparison with BRDF and atmospheric scattering corrections

Tiejun Chang, Xiaoxiong (Jack) Xiong, Graziela Keller, Xiangqian Wu

Proceedings Volume 10402, 1040223 (2017) https://doi.org/10.1117/12.2272784

KEYWORDS: Reflectivity, Satellites, Calibration, Bidirectional reflectance transmission function, Atmospheric corrections, MODIS, Sensors, Rayleigh scattering

Read Abstract +

The inter-comparison of the reflective solar bands between the instruments onboard a geostationary orbit satellite and onboard a low Earth orbit satellite is very helpful to assess their calibration consistency. GOES-R was launched on November 19, 2016 and Himawari 8 was launched October 7, 2014. Unlike the previous GOES instruments, the Advanced Baseline Imager on GOES-16 (GOES-R became GOES-16 after November 29 when it reached orbit) and the Advanced Himawari Imager (AHI) on Himawari 8 have onboard calibrators for the reflective solar bands. The assessment of calibration is important for their product quality enhancement. MODIS and VIIRS, with their stringent calibration requirements and excellent on-orbit calibration performance, provide good references. The simultaneous nadir overpass (SNO) and ray-matching are widely used inter-comparison methods for reflective solar bands. In this work, the inter-comparisons are performed over a pseudo-invariant target. The use of stable and uniform calibration sites provides comparison with appropriate reflectance level, accurate adjustment for band spectral coverage difference, reduction of impact from pixel mismatching, and consistency of BRDF and atmospheric correction. The site in this work is a desert site in Australia (latitude -29.0 South; longitude 139.8 East). Due to the difference in solar and view angles, two corrections are applied to have comparable measurements. The first is the atmospheric scattering correction. The satellite sensor measurements are top of atmosphere reflectance. The scattering, especially Rayleigh scattering, should be removed allowing the ground reflectance to be derived. Secondly, the angle differences magnify the BRDF effect. The ground reflectance should be corrected to have comparable measurements. The atmospheric correction is performed using a vector version of the Second Simulation of a Satellite Signal in the Solar Spectrum modeling and BRDF correction is performed using a semi-empirical model. AHI band 1 (0.47μm) shows good matching with VIIRS band M3 with difference of 0.15%. AHI band 5 (1.69μm) shows largest difference in comparison with VIIRS M10.

Proceedings Article | 19 October 2016 Paper

Model development for MODIS thermal band electronic cross-talk

Tiejun Chang, Aisheng Wu, Xu Geng, Yonghong Li, Jake Brinkmann, Graziela Keller, Xiaoxiong (Jack) Xiong

Proceedings Volume 10000, 100001Q (2016) https://doi.org/10.1117/12.2240515

KEYWORDS: MODIS, Sensors, Calibration, Temperature metrology, Contamination, Nonlinear response, Detector development, Signal detection, Photovoltaics, Mercury cadmium telluride

Read Abstract +

MODerate-resolution Imaging Spectroradiometer (MODIS) has 36 bands. Among them, 16 thermal emissive bands covering a wavelength range from 3.8 to 14.4 μm. After 16 years on-orbit operation, the electronic crosstalk of a few Terra MODIS thermal emissive bands develop substantial issues which cause biases in the EV brightness temperature measurements and surface feature contamination. The crosstalk effects on band 27 with center wavelength at 6.7 μm and band 29 at 8.5 μm increased significantly in recent years, affecting downstream products such as water vapor and cloud mask. The crosstalk issue can be observed from nearly monthly scheduled lunar measurements, from which the crosstalk coefficients can be derived. Most of MODIS thermal bands are saturated at moon surface temperatures and the development of an alternative approach is very helpful for verification. In this work, a physical model was developed to assess the crosstalk impact on calibration as well as in Earth view brightness temperature retrieval. This model was applied to Terra MODIS band 29 empirically for correction of Earth brightness temperature measurements. In the model development, the detector nonlinear response is considered. The impacts of the electronic crosstalk are assessed in two steps. The first step consists of determining the impact on calibration using the on-board blackbody (BB). Due to the detector nonlinear response and large background signal, both linear and nonlinear coefficients are affected by the crosstalk from sending bands. The crosstalk impact on calibration coefficients was calculated. The second step is to calculate the effects on the Earth view brightness temperature retrieval. The effects include those from affected calibration coefficients and the contamination of Earth view measurements. This model links the measurement bias with crosstalk coefficients, detector nonlinearity, and the ratio of Earth measurements between the sending and receiving bands. The correction of the electronic crosstalk can be implemented empirically from the processed bias at different brightness temperature. The implementation can be done through two approaches. As routine calibration assessment for thermal infrared bands, the trending over select Earth scenes is processed for all the detectors in a band and the band averaged bias is derived for certain time. In this case, the correction of an affected band can be made using the regression of the model with band averaged bias and then corrections of detector differences are applied. The second approach requires the trending for individual detectors and the bias for each detector is used for regression with the model. A test using the first approach was made for Terra MODIS band 29 with the biases derived from long-term trending of sea surface temperature and Dome-C surface temperature.

Showing 5 of 6 publications

View contact details

UPDATE YOUR PROFILE

Is this your profile? Update it now.

Sign into your SPIE.org account

Don’t have a profile and want one?

Create an account on SPIE.org

Keywords/Phrases

Search In:

Publication Years