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A NOVEL COMBINED OPTICAL 
METHOD FOR OBJECTIVELY MAP SOIL IN A NEAR REAL TIME DOMAIN 
E. Ben-Dor 3 *, K. Carmina 3 , D. Heller b and S. Chudnovsky c 
a The Geography and Human Environment Department 
Tel-Aviv University, Israel 
b Bar-Kal System Engineering’s ltd. Nethania, Israel 
department of Environmental Sciences and Energy Research, The Weizmann Institute, Rehovot, Israel 
Commission VI, WG VII/3 
KEY WORDS: Imaging Spectroscopy (IS), Penetrating Optical Sensing (POS), Soil mapping, Near Infrared Analysis (NIRS) 
ABSTRACT: 
The present study demonstrates a new concept for mapping soil, toward developing a semi-automated method to in situ classify soil. 
The concept is based on use of optical sensors that operate from both air and ground domains. The airborne sensor is based on 
imaging spectroscopy (IS) technology whereby every pixel in the image is characterized by a reflectance spectrum. The ground 
sensor is based on the Penetrating Optical Sensor (POS) technology whereby the optical head penetrates to the soil profde. This 
concept was examined over a selected field in Ashdod, a southern city in Israel. The IS data used was acquired from air scanner 
(AISA-ES) and POS data acquired from an ASD spectrometer over selected drill hole locations in a selected field. Five soil 
properties were evaluated at every drill hole depth using the Near Infra Red analysis approach (NIRS). The POS information 
enables obtaining an objective description of the soil profile, which was found to be more accurate than a traditional profile 
description using open trenches. For every selected point, six soil properties (specific surface area, organic matter, hygroscopic 
moisture, field moisture, carbonates, and iron oxide content) were evaluated. This information enables one to generate 5 depth 
layers (20-cm intervals) of the field by interpolating all points together. The 3D information provides new insight into the soils and 
opens up new frontiers for automatic soil mapping missions. Based on this study, further work is required in order to correlate the 
3D information obtained by the IS and POS with any soil classification nomenclature system (e.g., USDA). 
1. INTRODUCTION 
The conventional soil survey mission is performed by using 
extensive field observations (sometimes very subjective) and a 
follow-up laboratory analysis, which adds valuable 
information about the soil's properties in question (USDA, 
1999). The currently used classical soil survey is a rather 
complicated, expensive, and time- and money-consuming 
process. Consequently, there is a great demand for an 
alternative method to map soils rapidly and accurately. We 
suggest here to combine two spectral-based approaches to 
replace the conventional soil mapping process. They are as 
follows: 1) a ground approach based on the recent innovative 
method developed by Ben-Dor et al. (2008) that describes the 
soil profile by a Penetrating Optical Spectroscopy (POS) 
approach using fiber spectral assembly, ASD spectrometer, 
and NIRS models, and 2) an airborne approach that describes 
the soil surface by Imaging spectroscopy (IS) technology. The 
IS approach serves as a convenient method that might replace 
the traditional, ancient air photo method, providing cognitive 
and quantitative spatial views of the areas in question, and the 
POS may replace the wet laboratory measurements and the 
subjective field observation of open trenches. The purpose of 
this study is thus to demonstrate the integration between these 
two spectral-based methods (POS and IS) for mapping soil 
digitally, rapidly, and cost effectively in a 3D view. 
2. MATERIAL AND METHODS 
2.1. The Study Area 
An area of about 4000m 2 , characterized by alluvial soils, was 
selected to carry out this demonstration. The area is a bare filed 
situated in Ashdod, a southern city in Israel. Selected for its 
agriculture activity (seasonal wheat and cotton crops), the area 
was covered by one strip of the airborne imaging spectrometer, 
AISA-ES, and later also by conventional and POS soil survey 
approaches. 
2.2. Airborne Data 
The AISA-ES airborne sensor is a programmed imaging 
spectrometer consisting of two sensors mounted on the same 
optical bench and aligned to look at (almost) the same focal 
plane. The sensors are Eagle for the VIS region and Hawk for 
the SWIR region (See Speclm homepage at 
http://www.specim.fi/). We used 180 bands (60 in the VNIR and 
120 in the SWIR), which acquired information from 7,000 feet, 
providing a pixel size of 3 m. After the data acquisition (on 
August 2007), the raw data were converted into reflectance 
values using a combined ACRON and Empirical Line method. 
The reflectance obtained was validated against ground spectra 
of several selected targets. The reflectance image was used to 
generate a surface map that was based on the surface spectral 
information. 
2.3 POS - data 
The POS measurements were carried out by using a 3S-HED 
assembly (Sub Surface Spectral Head Device) to spectrally view 
and interpret the borehole’s walls from inside using fiber optic 
sensing and an illumination head. This device is hooked to a 25° 
bare fiber optic of an ASD field spectrometer that is sensitive to 
the VNIR-NIR spectral region (350-2500nm). The spectral 
information was modeled against the soil chemistry by using the 
NIRS approach (Ben-Dor and Banin, 1995). A detailed 
description of the 3S-HED concept can be found in Ben-Dor et 
al. (2008). Measurements were taken in intervals of 20cm from