Daniel Schläpfer

ReSe Applications LLC

Hyperspectral imaging technology holds great potential for various stages of the mining life cycle, both in active and abandoned mines, from exploration to reclamation. The technology, however, has yet to achieve large-scale industrial implementation and acceptance. While hyperspectral satellite imagery yields high spectral resolution, a high signa...

Increasing global plastic usage has raised critical concerns regarding marine pollution. This study addresses the pressing issue of floating marine macro-litter (FMML) by developing a novel monitoring system using a multi-spectral sensor and drones along the southern coast of South Korea. Subsequently, a convolutional neural network (CNN) model was...

Hyperspectral imaging data holds great potential for various stages of the mining life cycle in active and abandoned mines. The technology, however, has yet to achieve large-scale industrial implementation and acceptance. While hyperspectral satellite im-agery yields high spectral resolution, high signal-to-noise ratio (SNR), and global availabilit...

Hyperspectral imaging data holds great potential for the different stages of the mining life cycle in active and post-mining environments. However, the technology has yet to reach the stage of large-scale industrial implementation and acceptance. While hyperspectral satellite imagery can achieve high spectral resolution, signal-to-noise ratio (SNR)...

Classifiers trained on airborne hyperspectral imagery are proficient in identifying tree species in hyperdiverse tropical rainforests. However, spectral fluctuations, influenced by intrinsic and environmental factors, such as the heterogeneity of individual crown properties and atmospheric conditions, pose challenges for large-scale mapping. This s...

Surface reflectance is an important data product in imaging spectroscopy for obtaining surface information. The complex retrieval of surface reflectance, however, critically relies on accurate knowledge of atmospheric absorption and scattering, and the compensation of these effects. Furthermore, illumination and observation geometry in combination...

Hyperspectral instruments on UAV systems are increasingly used for extensive and repeated data acquisitions. This paper describes an efficient automatic atmospheric and topographic correction for such instruments. It is based on the DROACOR apparent reflectance outputs for flat terrain, which are further corrected for terrain illumination variation...

Thermal remote sensing from unmanned aerial vehicles is a slowly but steadily growing field of application. New hyperspectral systems operating in the thermal infrared are deployable on such systems and are also usable for ground based monitoring, such as in mining applications. Temperature/emissivity retrieval methods have to be adapted for these...

The acquisition of imaging spectroscopy data from ground based rotating stages is a novel approach which is more and more used in open pit mines for prospection and controlling. The special radiometric situation of such data sets asks for new processing approaches for geometric processing as well as for reflectance retrieval. Herein, a new method f...

The recent development of small form-factor (<6 kg), full range (400–2500 nm) pushbroom hyperspectral imaging systems (HSI) for unmanned aerial vehicles (UAV) poses a new range of opportunities for passive remote sensing applications. The flexible deployment of these UAV-HSI systems have the potential to expand the data acquisition window to accept...

In rugged terrain, topography substantially influences the illumination and observation geometry, and thus, the bidirectional reflectance distribution function (BRDF) of a surface. While this problem has been known and investigated for spaceborne optical data since the 1980s, it has led to several well-known topographic correction methods. To date,...

Remote sensing with unmanned aerial vehicles (UAVs) is a fast and cost-efficient tool for mapping and environmental monitoring. The sensors are operated at low flight altitudes, usually below 500 m above ground, leading to spatial resolutions up to the centimeter range. This type of data causes new challenges in atmospheric compensation and surface...

Masking of cirrus clouds in optical satellite imagery is an important step in automated processing chains. Firstly, it is a prerequisite to a subsequent removal of cirrus effects, and secondly, it affects the atmospheric correction, i.e., aerosol and surface reflectance retrievals. Cirrus clouds can be detected with a narrow bandwidth channel near...

Airborne hyper-spectral imaging has been proven to be an efficient means to provide new insights for the retrieval of biophysical variables. However, quantitative estimates of unbiased information derived from airborne hyperspectral measurements primarily require a correction of the anisotropic scattering properties of the land surface depicted by...

Remote imaging spectroscopy in the 0.4–2.5-μm visible and shortwave infrared (VSWIR) range captures the majority of solar-reflected energy and enables a wide range of earth surface studies. This spectral range is also influenced by atmospheric effects including absorption from atmospheric gases and aerosols, Rayleigh scattering, and particle scatte...

Imaging spectroscopy is a promising tool for airborne tree species recognition in hyper-diverse tropical canopies. However, its widespread application is limited by the signal sensitivity to acquisition parameters, which may require new training data in every new area of application. This study explores how various pre-processing steps may improve...

Fire radiative power (FRP) is a key product to quantify active fires, which indicates fuel consumption and fire emissions. In the case of the bispectral method, it can be calculated from remote sensing data if a midinfrared (3.8 μm) and thermal infrared channel (~10 μm) are available. While different uncertainty sources have been investigated, the...

In order to produce accurate and meaningful results from airborne hyperspectral data analysis, it is essential to have exact knowledge about the quality of the image data itself. Small differences in reflectance already produce diverse results particularly when it comes to vegetation analysis. Especially within the complex environment of forested a...

Physical atmospheric correction methods had first developed for the processing of satellite imagery and have become a standard processing step for such data at spatial resolutions between 1m and 50m .The concepts were further refined such that wide field of view airborne, specifically hyperspectral data can be processed on the basis of physical rad...

The atmospheric correction of optical remote sensing data requires the determination of aerosol and gas optical properties. A method is presented which allows the detection of the aerosol scattering effects from optical remote sensing data at spatial sampling intervals below 5 m in cloud-free situations from cast shadow pixels. The derived aerosol...

Imaging spectroscopy based methods offer unique capabilities for retrieving narrow-band vegetation indices which can be empirically related to functional traits of plants. However, in areas with complex topography, illumination effects affect the retrieval of such indices from high spatial resolution airborne or satellite data. Irradiance component...

The atmospheric correction accuracy strongly depends on the correct estimate of the aerosol scattering effects. This paper shows first results of a new aerosol optical thickness inversion method and its use for improved atmospheric correction of high spatial resolution imaging spectroscopy data. The approach uses small scale shadow pixels for the d...

Water vapor is one of the main parameters for atmospheric correction of Sentinel-2 imagery. Together with the aerosol retrieval it determines the accuracy of the surface reflectance product. Since Sentinel-2A and soon Sentinel-2B are operational satellites with a free data policy there is great interest in processing this data and using it for envi...

Field spectroscopy is increasingly used in various fields of science: either as a research tool in its own right or in support of airborne- or space-based optical instruments for calibration or validation purposes. Yet, while the use of the instruments appears deceptively simple, the processes of light and surface interactions are complex to be mea...

Multispectral satellite images are often contaminated by haze and/or cirrus. A previous paper presented a haze removal method that calculates a haze thickness map (HTM) based on a local search of dark objects. The haze-free signal is restored by subtracting the HTM from the hazy image assuming an additive model of the haze influence. The HTM method...

The spectral and radiometric quality of airborne imaging spectrometer data is affected by the anisotropic reflectance behavior of the imaged surface. Illumination and observation angle-dependent patterns of surface reflected radiation propagate into products, hinder quantitative assessment of biophysical/biochemical parameters, and decrease the com...

Recent developments in atmospheric compensation are summarized in this paper with emphasis on algorithms implemented in the ATCOR model. First, achievements and current limitations in haze and aerosol detection and correction as well as in BRDF correction are outlined. Secondly, correction approaches for high resolution spectral variations in the r...

The radiometric correction of airborne imagery aims at providing unbiased spectral information about the Earth’s surface. Correction steps include system calibration, geometric correction, and the compensation for atmospheric effects. Such preprocessed data are affected by the bidirectional reflectance distribution function (BRDF), which requires a...

We present the Airborne Prism Experiment (APEX), its calibration and subsequent radiometric measurements as well as Earth science applications derived from this data. APEX is a dispersive pushbroom imaging spectrometer covering the solar reflected wavelength range between 372 and 2540 nm with nominal 312 (max. 532) spectral bands. APEX is calibrate...

We present the Airborne Prism Experiment (APEX), its calibration and subsequent radiometric measurements as well as Earth science applications derived from this data. APEX is a dispersive pushbroom imaging spectrometer covering the solar reflected wavelength range between 372 and 2540 nm with nominal 312 (max. 532) spectral bands. APEX is calibrate...

Imaging spectroscopy (IS) provides an efficient tool to assess vegetation status and functioning at ecologically relevant scales. Reliable extraction of vegetation information from spatial and spectral high resolution spectroscopy data requires accurate retrieval schemes to account for the complex radiative transfer in the coupled vegetation-atmosp...

An accurate atmospheric correction (AC) of Earth remote-sensing data in the spectral region 450–800 nm has to account for the ozone gas absorption influence. Usual operational AC codes employ a fixed ozone concentration corresponding to a climatologic average for a certain region and season, e.g. the mid-latitude summer atmosphere of the Moderate R...

The generation of well-calibrated radiometric measurements from imaging spectrometer data requires careful consideration of all influencing factors, as well as an instrument calibration based on a detailed sensor model. Deviations of ambient parameters (i.e., pressure, humidity, temperature) from standard laboratory conditions during airborne opera...

The APEX airborne imaging spectrometer has been shown to exhibit spectral shifts during in-flight conditions, linked to changes in the nitrogen gas density within the APEX optical subunit. These shifts lead to features in the recorded spectra caused by the dichroic coating used as a beam splitter between VNIR and SWIR channels. Consequently dichroi...

Initial steps are proposed and tested in the development of a method for retrieving and (or) refining instrument spectral characteristics for dispersive hyperspeetral imagers such as the Airborne Visible / Infrared Imaging Spectrometer (AVIRIS), Compact Airborne Spectrographic Imager (cast), HyMap, Hyperion, and compact high-resolution imaging spec...

The new method for cast shadow detection has shown to significantly improve the topographic image correction. This method will be used for operational processing of remote sensing products based on the ADS systems operated by the Swiss Federal Institute of Topography (swisstopo) and will be available in future releases of the ATCOR software package...

Accurate spectral calibration of airborne and spaceborne imaging spectrometers is essential for proper preprocessing and scientific exploitation of high spectral resolution measurements of the land and atmosphere. A systematic performance assessment of onboard and scene-based methods for in-flight monitoring of instrument spectral calibration is pr...

This article presents the empirical research carried out in the context of the multi-site EuroSDR project "Radiometric aspects of digital photogrammetric images" and provides highlights of the results. The investigations have considered the vicarious radiometric and spatial resolution validation and calibration of the sensor system, radiometric pro...

Hyperspectral pushbroom imagers are affected by a number of artifacts, such as pixel nonuniformity, spectral smile, and keystone. These have to be taken into account during system correction, orthorectification, or atmospheric correction, as performed in processing and archiving facilities (PAFs). This contribution is presenting an efficient and ac...

Optical satellite images are often contaminated with cirrus clouds. Thin cirrus can be detected with a channel at 1.38 µm, and an established cirrus removal method exists for visible/near-infrared (VNIR) channels in atmospheric window regions which was demonstrated with MODIS (Moderate Resolution Imaging Spectrometer) data. This contribution addres...

The Airborne Prism EXperiment (APEX) is an airborne pushbroom imaging spectrometer for Earth observation. Its products will become available in 2011. APEX is currently prepared for final acceptance configuration completing final hardware upgrades, refined calibration methodologies and test flights. APEX is composed of an airborne dispersive pushbro...

Combining bidirectional-reflectance distribution functions of selected materials with airborne-laser and imaging-spectrometer data improves quantitative mapping accuracy.

ESA APEX (Airborne Prism EXperiment) is a project for the realisation of an airborne dispersive pushbroom imaging spectrometer, a dedicated data Processing and Archiving Facility (PAF, hosted at VITO) and a Calibration Home Base (CHB, hosted at DLR) for instrument calibration operation. It has been developed by a joint Swiss-Belgian consortium. The...

Sun-induced chlorophyll fluorescence (Fs) is a promising parameter for remote measuring plant photosynthesis. It has been demonstrated that Fs at cell and leaf level is strongly related to photosynthesis. The transfer of the Fs approach to canopy level remains challenging as the canopy Fs signal is not fully understood yet. Several factors influenc...

The transition from film imaging to digital imaging in photogrammetric data capture is opening interesting possibilities for photogrammetric processes. A great advantage of digital sensors is their radiometric potential. This article presents a state-of-the-art review on the radiometric aspects of digital photogrammetric images. The analysis is bas...

The correction of BRDF (bidirectional reflectance distribution function) effects in imaging spectrometer data requires object specific spectrodirectional information. Such data may be acquired using goniometer systems such as the dual-view Field Goniometer System (FIGOS). Their use in an operational processing environment requires optimized solutio...

An empirical (target-) BRDF normalization method has been implemented for Imaging Spectrometry data processing, following the approach of Kennedy, published in 1997. It is a simple, empirical method with the purpose of a rapid technique, based on a least-squares quadratic curve fitting process. The algorithm is calculating correction factors in eit...

This work is based on the method suggested for correction of reflectance anisotropy in imaging spectroscopy data, outlined at (i), using corresponding elevation data and multi-angular spectral measurements from a goniometer. We focus on the development of tools that can make Bidirectional Reflectance Distribution Function (BRDF) correction ready fo...

APEX (Airborne Prism EXperiment) is a project being developed by a joint Swiss-Belgian consortium on behalf of the European Space Agency ESA-PRODEX programme. It comprises an airborne dispersive pushbroom imaging spectrometer, a Calibration Home Base (CHB) for instrument calibration operations and a dedicated data Processing and Archiving Facility...

Detailed aerosol measurements in time and space are crucial to address open questions in climate research. Earth observation is a key instrument for that matter but it is biased by large uncertainties. Using airborne imaging spectroscopy, such as ESA's upcoming airborne Earth observing instrument APEX, allows determining the widely used aerosol opt...

With the advance of imaging spectroscopy systems, the correction of atmospheric influences has been continuously improved while adapting to the enhanced capabilities of current instruments. High resolutions airborne systems such as APEX, AISA, HYSPEX, and CASI-2/SASI have been developed, and powerful space systems such as ENMAP will soon be availab...

An empirical (target-) BRDF normalization method has been implemented for hyperspectral data processing, following the approach of Kennedy, published in 1997. Correction results of this method highly depend on the successful application of an appropriate spectral pre-classification which necessarily must be insensitive to reflectance anisotropy. A...

The product generation from hyperspectral sensor data has high requirements on the processing infrastructure, both hardware and software. The Airborne Prism Experiment (APEX) processing and archiving facility has been set up to provide for the automated generation of level-1 calibrated data and user-configurable on-demand product generation for hig...

The increasing quantity and sophistication of imaging spectroscopy applications have led to a higher demand on the quality of Earth observation data products. In particular, it is desired that data products be as consistent as possible (i.e., ideally uniform) in both spectral and spatial dimensions. Yet, data acquired from real (e.g., pushbroom) im...