# Retrieval of Biophysical Crop Variables from Multi-Angular Canopy Spectroscopy
## 5 Conclusions  
Spectral differences from a change in observation geometry depend on the optical properties of foliage and canopy. Complex architecture does not necessarily lead to an increased anisotropy, but the photochemistry of the leaf does very much so. With a step-wise hierarchical variable retrieval based on the PROSAIL model it was shown that longer path lengths do not lead to a higher accuracy in LAI estimation, but still allow a retrieval of this variable with satisfying accuracy. For LCC, on the other hand, the retrieval accuracy did increase when using off-nadir observations. Overall, accuracies are still in the range of about 20% for LAI and LCC. The look-up-table approach was improved when parameters were inverted hierarchically with educated a priori knowledge about the considered wavelengths. The implementation of a non-photosynthetic vegetation background improved the estimation of biophysical parameters especially for senescent phenology states. We agree with the authors of [58] in the assertion that there is no universal convention about the zenith view angles best suited to retrieve canopy structure from. For the final user, the following findings can be synthesized for winter wheat crops:  
* Effects of anisotropy are strongest for early phenological stages and backscatter observations;
* LAI is best estimated from near-nadir observations;
* Optimal results for a retrieval of leaf chlorophyll content is achieved for an observer zenith angle opposite to the sun (forward scatter);
* For both variables (LAI and LCC) feasible results are obtained for all considered EnMAP geometrical constellations.  
In summary, the off-nadir capability of the future EnMAP sensor will increase the number of available scenes for the user as well as the probability of achieving continuous time-series acquisitions.  
**Acknowledgments:** The research presented in this article was conducted at the Chair of Geography and Remote Sensing, Department of Geography, Ludwig-Maximilians-Universitat Munich. The financial support through the Space Administration of the German Aerospace Center (DLR) in the frame of the project \"EnMAP Scientific Advisory Group Phase II--Monitoring the Phenological Development of Agricultural Crops\" through funding by the German Ministry of Economics and Technology under the grant code 50 EE1308 is gratefully acknowledged. We want to thank the communal farms of Munich for granting access to the sampling plots and for providing auxiliary data.  
**Author Contributions:** [PERSON] wrote the code for the model inversion, conducted the analyses and wrote most of the manuscript. [PERSON] and [PERSON] assisted with the development of the inversion strategy and with the definition of the field sampling campaigns, [PERSON] helped with the field measurements, [PERSON] and [PERSON] contributed as supervisors. All authors contributed to the preparation of the manuscript.  
Conflicts of Interest: The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.