EXAMINATION OF ACCURACY AND RESOLUTION 
OF A HAND-HELD SPECTROMETER 
Andreas Fisler & Manfred Weisensee 
Institute of Applied Photogrammetry and Geoinformatics, 
University of Applied Sciences Oldenburg, D 26121 Oldenburg, Ofener Str. 16 
andreas.fisler@vermes.fh-oldenburg.de, weisensee@fh-oldenburg.de 
WG VII/1 Fundamentals Physics and Modelling 
KEY WORDS: Spectral, Calibration, Sensor, Pollution, Vegetation, Ecology, Agriculture 
ABSTRACT: 
Several applications for the examination of plants by use of hand-held spectrometers exist in the field of environmental monitoring 
and precision agriculture. Portable instruments render possible the measurement of the intensity of radiation in the range of 
approximately 350 nm to 950 nm with a spectral resolution of about 3 nm. Thus, they can be used for the spectral analysis of 
chemical elements in a laboratory, e.g. for chlorophyll analysis, but also for the mass screening of spectral reflectance of plants or 
parts of them in field work. Although field measurements cannot compete with a laboratory analysis concerning precision and 
reliability of the results, their application in a study is justified at least for coarse measurements but especially under the aspect of 
cost reduction. The reliable application of a hand-held spectrometer requires the examination of the spectral resolution and the 
accuracy of the intensity measurements. This papers describes a test procedure for a spectrometer based on calibrated cuvettes which 
are used for testing the state and the change of the instrument. The spectrometer is then applied in a study which aims at the 
detection of chemical elements, e.g. nutrients or heavy metal, in plants. 
1. INTRODUCTION 
The pressure on the environment caused by the emission of 
polluting substances has increased drastically since the 
Industrial Revolution. In areas with high industrial density the 
strain has already reached vast dimensions. Especially the 
pollution of soil in industrial waste land or in areas close to 
industrial plants can be extremely high so that a 
decontamination has to be carried out for any type of usage of 
the areas. 
Here, two different groups of contaminants have to be 
distinguished: 
e organic contaminants (oil, fat, military waste) and 
e metal, especially heavy metal like cadmium or lead. 
While for organic contaminants several well approved methods 
of decontamination are readily available, the extraction of metal 
from contaminated soil can only be accomplished by expensive 
procedures like extraction with acids, Fiedler 2001, or 
Phytoremediation. 
1.1 The Phytoremediation project 
Phytoremediation, i.e. the extraction of pollutants from soil by 
using plants, is an interesting alternative because the method 
offers several positive features: 
e In-situ application, 
e suitability for less or medium contaminated areas, 
e low costs and 
e maintenance of soil functionality, 
e but as a major disadvantage 
e decontamination of soil takes several years up to 
decades. 
88 
During such long periods of time the areas have to be monitored 
with suitable methods. Here, mobile hyper-spectral scanners 
can be applied for documenting the 
Phytoremediation under qualitative and quantitative aspects. 
The application of spectrometers in the research and industrial 
environment is increasing since several years. Due to expanding 
possibilities and falling prices a number of new applications 
came up: 
e Online process control, 
e Quality control, 
e Color management, 
e Qualitative and quantitative analysis in chemistry, 
pharmacy and biochemistry, 
e Precision farming, 
e Ground truth in Remote Sensing and 
e Medicine. 
The Institute for Applied Photogrammetry and Geoinformatics 
is currently participating in a research and development project 
which examines the performance of Phytoremediation 
measures. There, hyper-spectral sensors are applied for the 
detection of the effects and influence of specific chemical 
elements on the color of plants. 
1.2 The sensor 
Due to latest developments in the consumer sector several low- 
cost sensors with prices less then 3000 € are readily available. 
These hyper-spectral sensors in the VIS- to NIR-range are able 
to capture data in the range from up to 300 nm to 1000 nm with 
a resolution of some 3 to 5 nm with an accuracy of 5 to 10 %. 
This information is given by manufacturers and must be 
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