SPECTRO-DIRECTIONAL CHRIS/PROBA DATA OVER TWO SWISS TEST SITES FOR 
IMPROVED ESTIMATION OF BIOPHYSICAL AND -CHEMICAL VARIABLES 
- FIVE YEARS OF ACTIVITIES 
Mathias Kneubühler 3 , Benjamin Koetz ba , Silvia Huber ad , Niklaus E. Zimmermann c , Michael E. Schaepman d 
a RSL, Remote Sensing Laboratories, University of Zürich, Switzerland - (kneub, bkoetz, shuber)@geo.uzh.ch 
b ESA, European Space Agency, Frascati, Italy - Benjamin.Koetz@esa.int 
L WSL, Swiss Federal Research Institute, Birmensdorf, Switzerland - Niklaus.Zimmermann@wsl.ch 
d Centre for Geoinformation (CGI), Wageningen University and Research Centre, The Netherlands - 
Michael.Schaepman@wur.nl 
Commission VII, WG VII/1 
KEY WORDS: Ecosystem, Hyperspectral, Vegetation, Modelling, Monitoring, Retrieval, Spectral, Observations 
ABSTRACT: 
The spacebome ESA-mission CHRIS (Compact High Resolution Imaging Spectrometer) on-board PROBA-1 (Project for On-board 
Autonomy) delivers multi-directional data sets that contain spectral, directional, spatial and multi-temporal information. 
CHRIS/PROBA data have been acquired over two well documented test sites in Switzerland (Swiss National Park (SNP) and 
Vordemwald (VOR) since 2003 and allow for the monitoring of complex and dynamic vegetation canopies of forests and 
agricultural crops. For vegetated surfaces, the spectral information content of CHRIS/PROBA may yield the biochemical and 
biophysical properties of vegetation canopies, while the directional component may deliver additional information on canopy 
structure. The CHRIS instrument offers the possibility to combine independent information sources, such as spectral and directional 
observations, for a complete and robust characterization of a vegetation canopy. Such an integrated approach bears the potential to 
improve the estimation of biophysical and biochemical canopy characteristics relevant for applications such as ecological modeling 
and precision agriculture. A full pre-processing scheme for CHRIS/PROBA data for geometric and atmospheric processing over 
mountainous and hilly terrain, which is a pre-requisite for the subsequent spectro-directional data analysis, has been established. The 
three case studies presented in this paper deal with a) the assessment of canopy structure and heterogeneity from multi-angular data, 
b) the contribution of directional data for the estimation of canopy biochemistry and c) the estimation of leaf area index (LAI) from 
multi-temporal CHRIS/PROBA data. Concerning the first case study, the structure and heterogeneity of a coniferous canopy based 
on its degree of reflectance anisotropy is addressed using multi-angular CHRIS data and the parametric Rahman-Pinty-Verstraete 
(RPV) model. The second case study aims at an improved retrieval of foliar nitrogen concentration (C N ) and water content (C w ) 
using multi-angular CHRIS data and ground truth in multiple linear regression analyses limited by a statistical variable selection 
method. In the third case study, a radiative transfer model (RTM) is coupled to a canopy structure dynamics model (CSDM) for 
provision of a continuous LAI time course of maize over the season. The resulting estimation of the temporal and spatial variation of 
LAI is improved by integrating multi-temporal CHRIS/PROBA data and ground meteorological observations. The paper shows the 
potential and value of spectro-directional Earth observations, as provided by an innovative system like CHRIS/PROBA for Earth 
system studies. 
1. INTRODUCTION 
This paper presents three case studies that deal with the 
exploitation of spectral, directional, spatial and multi-temporal 
information contained in CHRIS/PROBA observations. The 
case studies present exemplarily the information content and 
thus the potential for improved vegetation characterization 
provided by an Earth observation mission such as 
CHRIS/PROBA sampling multiple information dimensions at 
Landsat-like spatial resolution. The work was carried out within 
the two well documented CHRIS/PROBA study sites that exist 
in Switzerland, namely the alpine Swiss National Park (SNP) 
and the Swiss Plateau study site Vordemwald (VOR) since 
2003. The three case studies presented in this paper deal with 1) 
the assessment of canopy structure and heterogeneity from 
multi-angular data, 2) the contribution of directional data for the 
estimation of canopy biochemistry and 3) the estimation of leaf 
area index, being a key variable for the understanding and 
modelling of several eco-physiological processes. The results 
clearly show the potential and value of spectro-directional Earth 
observations at regional scale for ecological monitoring and 
modeling studies. CHRIS/PROBA represents a rich source of 
information of Earth observation data specifically adapted for 
monitoring complex and dynamic vegetation canopies 
particularly in ecotones at the regional scale. 
2. DATA AND METHODS 
2.1 CHRIS/PROBA Data 
The CHRIS sensor on PROBA-1 provides spectral data over the 
visible/near-infrared spectral region from 400-1050 nm, and it 
can be operated at different modes reflecting on the one hand 
user needs and on the other hand a necessary compromise 
between spatial resolution and the number of spectral bands that 
can be stored onboard. The CHRIS sensor captures along-track 
five separate images of a given target area, whereas each image