Airborne Prism Experiment Calibration Information System

Hueni, Andreas; Lenhard, Karim; Baumgartner, Andreas; Schaepman, Michael E.

doi:10.1109/tgrs.2013.2246575

Cited by 35 publications

(22 citation statements)

References 24 publications

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“…The APEX Processing and Archiving Facility (PAF) was used to convert measured raw data streams into calibrated Level 1 at-sensor radiances [41,42]. Orthorectified, atmospherically and topographically corrected HemisphericalConical-Reflectance-Factor (HCRF) data were obtained from the at-sensor radiances using the PARGE (Parametric Geocorrection) [43] and the ATCOR-4 software [44].…”

Section: Airborne Prism Experiments (Apex)mentioning

confidence: 99%

Cross-Comparison of Albedo Products for Glacier Surfaces Derived from Airborne and Satellite (Sentinel-2 and Landsat 8) Optical Data

et al. 2017

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Surface albedo partitions the amount of energy received by glacier surfaces from shortwave fluxes and modulates the energy available for melt processes. The ice-albedo feedback, influenced by the contamination of bare-ice surfaces with light-absorbing impurities, plays a major role in the melting of mountain glaciers in a warming climate. However, little is known about the spatial and temporal distribution and variability of bare-ice glacier surface albedo under changing conditions. In this study, we focus on two mountain glaciers located in the western Swiss Alps and perform a cross-comparison of different albedo products. We take advantage of high spectral and spatial resolution (284 bands, 2 m) imaging spectrometer data from the Airborne Prism Experiment (APEX) and investigate the applicability and potential of Sentinel-2 and Landsat 8 data to derive broadband albedo products. The performance of shortwave broadband albedo retrievals is tested and we assess the reliability of published narrow-to-broadband conversion algorithms. The resulting albedo products from the three sensors and different algorithms are further cross-compared. Moreover, the impact of the anisotropy correction is analysed depending on different surface types. While degradation of the spectral resolution impacted glacier-wide mean albedo by about 5%, reducing the spatial resolution resulted in changes of less than 1%. However, in any case, coarser spatial resolution was no longer able to represent small-scale variability of albedo on glacier surfaces. We discuss the implications when using Sentinel-2 and Landsat 8 to map dynamic glaciological processes and to monitor glacier surface albedo on larger spatial and more frequent temporal scales.

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Section: Airborne Prism Experiments (Apex)mentioning

confidence: 99%

Cross-Comparison of Albedo Products for Glacier Surfaces Derived from Airborne and Satellite (Sentinel-2 and Landsat 8) Optical Data

et al. 2017

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“…in combination with an instantaneous field of view (FOV) of 0.0025°resulted in a surface projected pixel resolution of~2 m. APEX is a dispersive pushbroom imaging spectrometer, covering the spectral wavelength range between 400-2500 nm in 313 narrow continuous spectral bands . Radiometric and spectral calibration of measured raw signals was done using the APEX Processing and Archiving Facility (PAF), allowing us to convert raw data streams into calibrated level 1 at-sensor radiances (Hueni, Lenhard, Baumgartner, & Schaepman, 2013;Jehle et al, 2010). Calibrated radiances were subsequently orthorectified using the Parametric Geocorrection (PARGE) software ) and a combined atmospheric/topographic correction was applied using the ATCOR-4 software to obtain Hemispherical-Conical-Reflectance Factor (HCRF) data .…”

Section: Airborne Spectroscopymentioning

confidence: 99%

Imaging spectroscopy to assess the composition of ice surface materials and their impact on glacier mass balance

Naegeli

Damm

Huss

et al. 2015

Remote Sensing of Environment

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Glacier surfaces are not only composed of ice or snow but are heterogeneous mixtures of different materials. The occurrence and dynamics of light-absorbing impurities affect ice surface characteristics and strongly influence glacier melt processes. However, our understanding of the spatial distribution of impurities and their impact on ice surface characteristics and the glacier's energy budget is still limited. We use imaging spectroscopy in combination with in-situ experiments to assess the composition of ice surface materials and their respective impact on surface albedo and glacier melt rates. Spectroscopy data were acquired in August 2013 using the Airborne Prism EXperiment (APEX) imaging spectrometer and were used to map the abundances of six predominant surface materials on Glacier de la Plaine Morte, Swiss Alps. A pixel-based classification revealed that about 10% of the ice surface is covered with snow, water or debris. The remaining 90% of the surface can be divided into three types of glacier ice, namely~7% dirty ice,~43% pure ice and~39% bright ice. Spatially distributed spectral albedo derived from APEX reflectance data in combination with in-situ multi-angular spectroscopic measurements was used to analyse albedo patterns present on the glacier surface. About 85% of all pixels exhibit a low albedo between 0.1 and 0.4 (mean albedo 0.29 ± 0.12), indicating that Glacier de la Plaine Morte is covered with a significant amount of light-absorbing impurities, resulting in a strong ice-albedo feedback during the ablation season. Using a pixel-based albedo map instead of a constant albedo for ice (0.34) as input for a mass balance model revealed that the glacier-wide total ablation remained similar (10% difference). However, the large local variations in mass balance can only be reproduced using the pixel-based albedo derived from APEX, emphasizing the need to quantify spatial albedo differences as an important input for glacier mass balance models.

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“…It measures backscattered solar irradiance in the visible and near-infrared (VNIR) and in the short-wave infrared (SWIR) with a high spatial and spectral resolution (see Table 1 for spectrometer characteristics). The instrument is calibrated regularly in ground calibration facilities [12,13], and an in-flight calibration facility can be used before and after data acquisition to improve the spectral calibration using a quartz tungsten halogen lamp and four spectral filters [14]. D'Odorico et al [14] determined APEX's spectral calibration parameters for different flight altitudes, i.e., different temperature and pressure conditions, using oxygen and water absorption lines, thus focusing on the near-and short-wave infrared.…”

Section: Introductionmentioning

confidence: 99%

An Algorithm for In-Flight Spectral Calibration of Imaging Spectrometers

et al. 2016

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Accurate spectral calibration of satellite and airborne spectrometers is essential for remote sensing applications that rely on accurate knowledge of center wavelength (CW) positions and slit function parameters (SFP). We present a new in-flight spectral calibration algorithm that retrieves CWs and SFPs across a wide spectral range by fitting a high-resolution solar spectrum and atmospheric absorbers to in-flight radiance spectra. Using a maximum a posteriori optimal estimation approach, the quality of the fit can be improved with a priori information. The algorithm was tested with synthetic spectra and applied to data from the APEX imaging spectrometer over the spectral range of 385-870 nm. CWs were retrieved with high accuracy (uncertainty <0.05 spectral pixels) from Fraunhofer lines below 550 nm and atmospheric absorbers above 650 nm. This enabled a detailed characterization of APEX's across-track spectral smile and a previously unknown along-track drift. The FWHMs of the slit function were also retrieved with good accuracy (<10% uncertainty) for synthetic spectra, while some obvious misfits appear for the APEX spectra that are likely related to radiometric calibration issues. In conclusion, our algorithm significantly improves the in-flight spectral calibration of APEX and similar spectrometers, making them better suited for the retrieval of atmospheric and surface variables relying on accurate calibration.

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Airborne Prism Experiment Calibration Information System

Cited by 35 publications

References 24 publications

Cross-Comparison of Albedo Products for Glacier Surfaces Derived from Airborne and Satellite (Sentinel-2 and Landsat 8) Optical Data

Cross-Comparison of Albedo Products for Glacier Surfaces Derived from Airborne and Satellite (Sentinel-2 and Landsat 8) Optical Data

Imaging spectroscopy to assess the composition of ice surface materials and their impact on glacier mass balance

An Algorithm for In-Flight Spectral Calibration of Imaging Spectrometers

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