AirSpex 2007

1. Introduction

 

Remote sensing consists of a wide range of different instruments and techniques. AirSpex 2007 focuses mainly on hyperspectral imaging and related analyzing methods of the data. The aim of the applications of the multi purpose spectral imager is to produce two-dimensional images of distant objects at as many different visible wavelengths as possible with a usable spatial and spectral resolution. This three-dimensional data volume may then be used in image classification, which is a powerful tool in remote sensing.

 

The AirSpex 2007 flight campaign is part of the UNIS course "AGF-331 Remote Sensing and Spectroscopy". The plan for the flight campaign was to concentrate on two target sites on Svalbard: Longyearbyen and the deserted Russian settlement of Pyramiden. Combining suitable weather conditions with flight windows of the airplane turned out to be impossible this year and the only observations which were undertaken were of Longyearbyen, from a helicopter.

 

The program of AirSpex 2007 was carried out with two different platforms. The main part of the project was to use helicopter SA 365 N2 from Airlift AS, and similar instruments as used in the previous years’ flight campaigns. During earlier years of AirSpex campaigns observations have been carried out from an airplane (the Dornier from Lufttransport AS), so this year's observations with helicopter mounted instruments were the first of their kind. The instrument setup consists of a hyperspectral imaging spectrograph, a webcamera for logging purposes and Nikon D200 SLR camera for high resolution images of the ground.

 

The second platform which was tried out was the UAV/drone from Norut IT, with a similar spectrometer setup (DRONESPEX) as in the main instrument setup in the helicopter. The UAV called "Otto" has been used also in AirSpex 2006 campaign and in 2007 a new version was introduced.

 

In the following chapters, the reader is expected to have a basic knowledge of the names and locations of the buildings in central Longyearbyen, Svalbard. 

 

Basic principles of imaging spectroscopy

 

Spectroscopy has many applications. One of these is imaging spectroscopy (hyperspectral imaging), where an image is generated in a specific wavelength. The instrument used is a passive instrument, so in order to generate an image the instrument has to be moved according to the target. Figure 1.1 shows a schematic drawing of the instrument, which will be described in more detail in the next chapter. Basically, the spectrograph is working by light that comes through the entrance slit (S), gets collected in the first lens (L2), then dispersed in the grism (P) and align by the second lens (L3) before getting recorded by the CCD-chip.             

 

 

Figure 1.1: (A) Simple outline of a spectrograph, showing the front optics(L1), entrance slit (S), collector lens (L2),  grism (P), camera lens (L3) and CCD. (B) Parameter associated with spectroscopy measurements done in an airborne campaign. From [1]. 

 

The grism is the important part of the instrument. It is a prism with a graving on it, and thus, it disperses the light without preferred wavelengths.

Snell’s law can be used for describing the dispersion of a grating.

where m is the spectral order, is the wavelength , a is the groove spacing, is the incident angle and is the diffracted angle. The refractive index of a prism is given by Cauchy’s equation

where A and B are constants. From these two equations the angular dispersion of the grism can be calculated

,

[1].

The detector of the instrument is a commercial CCD-chip so it is made for recording in the visible area from 450 to 800 nm. This area can be divided into  colours, which is depictured in Figure 1.2.  

Figur 1.2          The colours of visible light. [2]

 

References

[1] Airborne Hyperspectral Imaging, F. Sigernes, 2005.

[2] Physics of color, Wikipedia, 2007, http://en.wikipedia.org/wiki/Color

 

FLIGHTS

DATA ANALYSIS