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Abstract

This paper presents results of using multi-sensor and multi-angular constraints in the generic Earth Observation-Land Data Assimilation
System (EO-LDAS) for reproducing arbitrary bandsets of hyperspectral reflectance at the top-of-canopy (TOC) level by merging observations
from multispectral sensors with different spectral characteristics. This is demonstrated by combining Multi-angle Imaging Spectroradiometer
(MISR) and Landsat Enhanced Thematic Mapper Plus (ETM+) data to simulate the Compact High Resolution Imaging
Spectrometer CHRIS/PROBA hyperspectral signal over an agricultural test site, in Barrax, Spain. However, the method can be more generally
applied to any combination of spectral data, providing a tool for merging EO data to any arbitrary hyperspectral bandset.
Comparisons are presented using both synthetic and observed MISR and Landsat data, and retrieving surface biophysical properties.
We find that when using simulated MISR and Landsat data, the CHRIS/PROBA hyperspectral signal is reproduced with RMSE 0.0001–
0.04. LAI is retrieved with r2 from 0.97 to 0.99 and RMSE of from 0.21 to 0.38. The results based on observed MISR and Landsat data
have lower performances, with RMSE for the reproduced CHRIS/PROBA hyperspectral signal varying from 0.007 to 0.2. LAI is
retrievedwith r2 from 0.7 to 0.9 and RMSE from 0.7 to 1.4. We found that for the data considered here the main spectral variations
in the visible and near infrared regions can be described by a limited number of parameters (3–4) that can be estimated from multispectral
information. Results show that the method can be used to simulate arbitrary bandsets, which will be of importance to any application
which requires combining new and existing streams of new EO data in the optical domain, particularly intercalibration of EO satellites in
order to get continuous time series of surface reflectance, across programmes and sensors of different designs.