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Sensors 2011, 11(8), 7476-7501; doi:10.3390/s110807476
Article

Characterizing Olive Grove Canopies by Means of Ground-Based Hemispherical Photography and Spaceborne RADAR Data

1,* , 1
, 2
, 1
 and 1
1 ETSITGC, Technical University of Madrid, Campus SUR, Ctra. de Valencia, km.7, Madrid 28031, Spain 2 Facultad de Ciencias Biológicas y Ambientales, Area de Geodinámica Externa, Campus de Vegazana, Universidad de León, León 24071, Spain
* Author to whom correspondence should be addressed.
Received: 24 June 2011 / Revised: 20 July 2011 / Accepted: 21 July 2011 / Published: 28 July 2011
(This article belongs to the Special Issue Sensors in Agriculture and Forestry)

Abstract

One of the main strengths of active microwave remote sensing, in relation to frequency, is its capacity to penetrate vegetation canopies and reach the ground surface, so that information can be drawn about the vegetation and hydrological properties of the soil surface. All this information is gathered in the so called backscattering coefficient (s0). The subject of this research have been olive groves canopies, where which types of canopy biophysical variables can be derived by a specific optical sensor and then integrated into microwave scattering models has been investigated. This has been undertaken by means of hemispherical photographs and gap fraction procedures. Then, variables such as effective and true Leaf Area Indices have been estimated. Then, in order to characterize this kind of vegetation canopy, two models based on Radiative Transfer theory have been applied and analyzed. First, a generalized two layer geometry model made up of homogeneous layers of soil and vegetation has been considered. Then, a modified version of the Xu and Steven Water Cloud Model has been assessed integrating the canopy biophysical variables derived by the suggested optical procedure. The backscattering coefficients at various polarized channels have been acquired from RADARSAT 2 (C-band), with 38.5° incidence angle at the scene center. For the soil simulation, the best results have been reached using a Dubois scattering model and the VV polarized channel (r2 = 0.88). In turn, when effective LAI (LAIeff) has been taken into account, the parameters of the scattering canopy model are better estimated (r2 = 0.89). Additionally, an inversion procedure of the vegetation microwave model with the adjusted parameters has been undertaken, where the biophysical values of the canopy retrieved by this methodology fit properly with field measured values.
Keywords: active remote sensing; RADARSAT 2; soil roughness; soil moisture; backscattering coefficient; microwave scattering models; hemispherical photography; Gap Fraction; Leaf Area Index (LAI) active remote sensing; RADARSAT 2; soil roughness; soil moisture; backscattering coefficient; microwave scattering models; hemispherical photography; Gap Fraction; Leaf Area Index (LAI)
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Molina, I.; Morillo, C.; García-Meléndez, E.; Guadalupe, R.; Roman, M.I. Characterizing Olive Grove Canopies by Means of Ground-Based Hemispherical Photography and Spaceborne RADAR Data. Sensors 2011, 11, 7476-7501.

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