26 research outputs found
Atmospheric Correction Performance of Hyperspectral Airborne Imagery over a Small Eutrophic Lake under Changing Cloud Cover
Atmospheric correction of remotely sensed imagery of inland water bodies is essential
to interpret water-leaving radiance signals and for the accurate retrieval of water quality variables.
Atmospheric correction is particularly challenging over inhomogeneous water bodies surrounded by
comparatively bright land surface. We present results of AisaFENIX airborne hyperspectral imagery
collected over a small inland water body under changing cloud cover, presenting challenging but
common conditions for atmospheric correction. This is the first evaluation of the performance of
the FENIX sensor over water bodies. ATCOR4, which is not specifically designed for atmospheric
correction over water and does not make any assumptions on water type, was used to obtain
atmospherically corrected reflectance values, which were compared to in situ water-leaving
reflectance collected at six stations. Three different atmospheric correction strategies in ATCOR4
was tested. The strategy using fully image-derived and spatially varying atmospheric parameters
produced a reflectance accuracy of �0.002, i.e., a difference of less than 15% compared to the in situ
reference reflectance. Amplitude and shape of the remotely sensed reflectance spectra were in general
accordance with the in situ data. The spectral angle was better than 4.1� for the best cases, in the
spectral range of 450–750 nm. The retrieval of chlorophyll-a (Chl-a) concentration using a popular
semi-analytical band ratio algorithm for turbid inland waters gave an accuracy of ~16% or 4.4 mg/m3
compared to retrieval of Chl-a from reflectance measured in situ. Using fixed ATCOR4 processing
parameters for whole images improved Chl-a retrieval results from ~6 mg/m3 difference to reference
to approximately 2 mg/m3. We conclude that the AisaFENIX sensor, in combination with ATCOR4
in image-driven parametrization, can be successfully used for inland water quality observations.
This implies that the need for in situ reference measurements is not as strict as has been assumed and
a high degree of automation in processing is possible
NEW LIGHT-WEIGHT STEREOSOPIC SPECTROMETRIC AIRBORNE IMAGING TECHNOLOGY FOR HIGH-RESOLUTION ENVIRONMENTAL REMOTE SENSING – CASE STUDIES IN WATER QUALITY MAPPING
A new Fabry-Perot interferometer (FPI) based light-weight spectrometric camera provides new possibilities for environmental
remote sensing applications. The sensor collects spectral data cubes with adjustable spectral properties in a rectangular image format,
and so stereoscopic data can be obtained by gathering images in block structures with overlapping images. The FPI camera thus
enables stereoscopic, spectrometric remote sensing applications with light-weight, low-cost airborne imaging systems. Our objective
is to investigate the processing and use of this new imaging technology in a water quality mapping. We carried out imaging
campaigns over a small lake in summer and autumn 2012 using a light-weight unmanned airborne vehicle (UAV) and a small
manned airborne vehicle (MAV). We present the preliminary results of these campaigns
METROLOGY OF IMAGE PROCESSING IN SPECTRAL REFLECTANCE MEASUREMENT BY UAV
Remote sensing based on unmanned airborne vehicles (UAVs) is rapidly developing field of technology. For many of potential UAV remote sensing applications, accurate reflectance measurements are required. Overall objective of our investigation is to develop a SI-traceable procedure for reflectance measurement using spectrometric image data collected by an UAV. In this article, our objective is to investigate the uncertainty propagation of image data post-processing. We will also present the first results of three traceable UAV remote sensing campaigns
Geometric processing workflow for vertical and oblique hyperspectral frame images collected using UAV
Remote sensing based on unmanned airborne vehicles (UAVs) is a rapidly developing field of technology. UAVs enable accurate,
flexible, low-cost and multiangular measurements of 3D geometric, radiometric, and temporal properties of land and vegetation
using various sensors. In this paper we present a geometric processing chain for multiangular measurement system that is designed
for measuring object directional reflectance characteristics in a wavelength range of 400–900 nm. The technique is based on a novel,
lightweight spectral camera designed for UAV use. The multiangular measurement is conducted by collecting vertical and oblique
area-format spectral images. End products of the geometric processing are image exterior orientations, 3D point clouds and digital
surface models (DSM). This data is needed for the radiometric processing chain that produces reflectance image mosaics and
multiangular bidirectional reflectance factor (BRF) observations. The geometric processing workflow consists of the following three
steps: (1) determining approximate image orientations using Visual Structure from Motion (VisualSFM) software, (2) calculating
improved orientations and sensor calibration using a method based on self-calibrating bundle block adjustment (standard
photogrammetric software) (this step is optional), and finally (3) creating dense 3D point clouds and DSMs using Photogrammetric
Surface Reconstruction from Imagery (SURE) software that is based on semi-global-matching algorithm and it is capable of
providing a point density corresponding to the pixel size of the image. We have tested the geometric processing workflow over
various targets, including test fields, agricultural fields, lakes and complex 3D structures like forests
Radiometric correction of multitemporal hyperspectral uas image mosaics of seedling stands
cited By 0; Conference of 2017 Frontiers in Spectral imaging and 3D Technologies for Geospatial Solutions ; Conference Date: 25 October 2017 Through 27 October 2017; Conference Code:131286Novel miniaturized multi- and hyperspectral imaging sensors on board of unmanned aerial vehicles have recently shown great potential in various environmental monitoring and measuring tasks such as precision agriculture and forest management. These systems can be used to collect dense 3D point clouds and spectral information over small areas such as single forest stands or sample plots. Accurate radiometric processing and atmospheric correction is required when data sets from different dates and sensors, collected in varying illumination conditions, are combined. Performance of novel radiometric block adjustment method, developed at Finnish Geospatial Research Institute, is evaluated with multitemporal hyperspectral data set of seedling stands collected during spring and summer 2016. Illumination conditions during campaigns varied from bright to overcast. We use two different methods to produce homogenous image mosaics and hyperspectral point clouds: image-wise relative correction and image-wise relative correction with BRDF. Radiometric datasets are converted to reflectance using reference panels and changes in reflectance spectra is analysed. Tested methods improved image mosaic homogeneity by 5% to 25%. Results show that the evaluated method can produce consistent reflectance mosaics and reflectance spectra shape between different areas and dates. © Authors 2017.Novel miniaturized multi- and hyperspectral imaging sensors on board of unmanned aerial vehicles have recently shown great potential in various environmental monitoring and measuring tasks such as precision agriculture and forest management. These systems can be used to collect dense 3D point clouds and spectral information over small areas such as single forest stands or sample plots. Accurate radiometric processing and atmospheric correction is required when data sets from different dates and sensors, collected in varying illumination conditions, are combined. Performance of novel radiometric block adjustment method, developed at Finnish Geospatial Research Institute, is evaluated with multitemporal hyperspectral data set of seedling stands collected during spring and summer 2016. Illumination conditions during campaigns varied from bright to overcast. We use two different methods to produce homogenous image mosaics and hyperspectral point clouds: image-wise relative correction and image-wise relative correction with BRDF. Radiometric datasets are converted to reflectance using reference panels and changes in reflectance spectra is analysed. Tested methods improved image mosaic homogeneity by 5% to 25%. Results show that the evaluated method can produce consistent reflectance mosaics and reflectance spectra shape between different areas and dates. © Authors 2017.Peer reviewe
ASSESSMENT OF VARIOUS REMOTE SENSING TECHNOLOGIES IN BIOMASS AND NITROGEN CONTENT ESTIMATION USING AN AGRICULTURAL TEST FIELD
Multispectral and hyperspectral imaging is usually acquired by satellite and aircraft platforms. Recently, miniaturized hyperspectral 2D frame cameras have showed great potential to precise agriculture estimations and they are feasible to combine with lightweight platforms, such as drones. Drone platform is a flexible tool for remote sensing applications with environment and agriculture. The assessment and comparison of different platforms such as satellite, aircraft and drones with different sensors, such as hyperspectral and RGB cameras is an important task in order to understand the potential of the data provided by these equipment and to select the most appropriate according to the user applications and requirements. In this context, open and permanent test fields are very significant and helpful experimental environment, since they provide a comparative data for different platforms, sensors and users, allowing multi-temporal analyses as well. Objective of this work was to investigate the feasibility of an open permanent test field in context of precision agriculture. Satellite (Sentinel-2), aircraft and drones with hyperspectral and RGB cameras were assessed in this study to estimate biomass, using linear regression models and in-situ samples. Spectral data and 3D information were used and compared in different combinations to investigate the quality of the models. The biomass estimation accuracies using linear regression models were better than 90 % for the drone based datasets. The results showed that the use of spectral and 3D features together improved the estimation model. However, estimation of nitrogen content was less accurate with the evaluated remote sensing sensors. The open and permanent test field showed to be suitable to provide an accurate and reliable reference data for the commercial users and farmers