Header

UZH-Logo

Maintenance Infos

Estimating nitrogen concentration from directional CHRIS/PROBA data


Huber, S; Kneubühler, Mathias; Koetz, Benjamin; Schopfer, Jürg (2007). Estimating nitrogen concentration from directional CHRIS/PROBA data. In: ISPRS Working Group VII/1 Workshop ISPMSRS'07: "Physical Measurements and Signatures in Remote Sensing" , Davos (CH), 12 March 2007 - 14 March 2007.

Abstract

Sun and sensor geometry cause directional effects in remotely sensed reflectance data which can influence the estimation of biophysical and biochemical variables. Previous studies have indicated that bidirectional measurements contain added information with which the accuracy of derived plant structural parameters can be increased. Because accurate biochemistry mapping is linked to vegetation structure, nitrogen concentration (CN) estimates might be indirectly improved with multiangular information. We analyzed data of the spaceborne ESA-mission CHRIS on-board PROBA-1, which provides hyperspectral and multiangular data. The images were acquired in July 2006 over a forest study site in Switzerland and were subsequently preprocessed. From each of the five CHRIS images (five different viewing zenith angles) we extracted 60 crown spectra, which correspond to field-sampled trees. Then we developed four-term models by regressing lab-measured CN on four datasets either consisting of original reflectance values (SPEC) or continuum-removed data. The wavebands used in the regression models were determined with a subset selection algorithm. For the data of all view angle combinations particular models were generated, in total 31 equations were evaluated per spectral dataset by comparing the coefficients of determination (R2) and cross-validated root mean square errors. The results of this study indicate that added information contained in multiangular data improved regression models for CN estimation and lowered RMS errors. Considerable contribution can be achieved with data of a second and third viewing zenith angle. Models based on combinations of off-nadir data performed best. These findings support the potential of multiangular Earth observations for ecological monitoring and modeling studies.

Abstract

Sun and sensor geometry cause directional effects in remotely sensed reflectance data which can influence the estimation of biophysical and biochemical variables. Previous studies have indicated that bidirectional measurements contain added information with which the accuracy of derived plant structural parameters can be increased. Because accurate biochemistry mapping is linked to vegetation structure, nitrogen concentration (CN) estimates might be indirectly improved with multiangular information. We analyzed data of the spaceborne ESA-mission CHRIS on-board PROBA-1, which provides hyperspectral and multiangular data. The images were acquired in July 2006 over a forest study site in Switzerland and were subsequently preprocessed. From each of the five CHRIS images (five different viewing zenith angles) we extracted 60 crown spectra, which correspond to field-sampled trees. Then we developed four-term models by regressing lab-measured CN on four datasets either consisting of original reflectance values (SPEC) or continuum-removed data. The wavebands used in the regression models were determined with a subset selection algorithm. For the data of all view angle combinations particular models were generated, in total 31 equations were evaluated per spectral dataset by comparing the coefficients of determination (R2) and cross-validated root mean square errors. The results of this study indicate that added information contained in multiangular data improved regression models for CN estimation and lowered RMS errors. Considerable contribution can be achieved with data of a second and third viewing zenith angle. Models based on combinations of off-nadir data performed best. These findings support the potential of multiangular Earth observations for ecological monitoring and modeling studies.

Statistics

Downloads

36 downloads since deposited on 08 May 2013
11 downloads since 12 months
Detailed statistics

Additional indexing

Item Type:Conference or Workshop Item (Paper), not refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Geography
Dewey Decimal Classification:910 Geography & travel
Language:English
Event End Date:14 March 2007
Deposited On:08 May 2013 12:24
Last Modified:05 Apr 2016 16:46
Publisher:ISPRS
Free access at:Official URL. An embargo period may apply.
Official URL:http://www.isprs.org/proceedings/XXXVI/7-C50/papers/P80.pdf
Related URLs:http://www.isprs.org/proceedings/XXXVI/7-C50/ (Publisher)

Download

Preview Icon on Download
Preview
Content: Published Version
Language: English
Filetype: PDF
Size: 1MB

TrendTerms

TrendTerms displays relevant terms of the abstract of this publication and related documents on a map. The terms and their relations were extracted from ZORA using word statistics. Their timelines are taken from ZORA as well. The bubble size of a term is proportional to the number of documents where the term occurs. Red, orange, yellow and green colors are used for terms that occur in the current document; red indicates high interlinkedness of a term with other terms, orange, yellow and green decreasing interlinkedness. Blue is used for terms that have a relation with the terms in this document, but occur in other documents.
You can navigate and zoom the map. Mouse-hovering a term displays its timeline, clicking it yields the associated documents.

Author Collaborations