PRE LOCATION MEASUREMENTS FOR
NEW AURORAL STATION ON SVALBARD,
NORWAY

Fred Sigernes, Dag A. Lorentzen, Stefan Claes and Nikita Shumilov

University Courses on Svalbard (UNIS), Box. 156, N-9171 Longyearbyen, Norway

Abstract
The Auroral station in Adventdalen close to Longyearbyen (78 N,15 E) suffers from increasing light pollution due to the towns growing numbers of buildings and use of street lights. In order to select a new optimal site for auroral ground-based optical measurements, images have been taken from two selected sites (Breinosa and Platåberget)  to documents light pollution and the field of view (Sky view). A camera system with GPS and gyros was constructed to get pitch, roll and yaw angles together with geographical position. The system was mounted onto an all-terrain belt mobile owned be the Governor of Svalbard. Data from the instrument and a short summary are presented. The best location was found to be Breinosa.

1. INTRODUCTION
The Auroral Station in Adventdalen was built in 1978 and has been used as an optical site for ground-based observations of the dayside and  night side aurora in the polar cap. The station is located about 4 km East of Longyearbyen. Figure 1. shows a photograph of the station.  The station is in daytime located underneath the average dayside aurora oval. The two months of astronomical darkness at mid-winter makes the location to one of the most ideal sites for ground-based observations of the daytime aurora in the world. 


Figure 1. Back side view of the Auroral Station in Adventdalen.

The station has a fairly large group of high resolution, low light level optical instruments. Data from these instruments have been used widely in publications throughout the last two decades of auroral / space research. Look at Sigernes et al. (2002)  for more information about the station (populist overview). In recent years Longyearbyen has increased in size and population. As a consequence, the use of light is also dramatically increased. During partly clouded weather, light are scattered into the field of view of the stations instruments. Especially our all sky imagers suffers from this pollution. In addition, clear sky spectroscopic measurements records emission lines originating from street lights that are scattered from a height of about 4 km above town. Direct illumination of the station by cars are also an increasing problem, but not as serious as the town lights, as it is more restricted to certain time periods of the day.

Furthermore, the activity at the station has steadily increased during the past decade. The station board has not been able to accommodate all requests for research activity. The need for more and better space will very soon limit further expansion. As a consequence, a process has been initiated to build a new station. Two sites are discussed in terms of background light levels (light pollution from Longyearbyen) and field of view (sky view). The first site is Breinosa close to Mine 7, 12.4 km South-East of Longyearbyen. The second site is Platåberget where the SVALSAT satellite station is located (5.6 km East of Longyearbyen, close to the airport). Both sites are 520 m above sea level. Note that the station is 4.7 km from Longyearbyen. The instrument used to visualize both light pollution and sky view is presented together with data and a short summary. 

2. TECHNIQUE / INSTRUMENT: THE 3DM-INS
The instrument used in this investigation was constructed as a prototype through the Gyro project together with STATOIL. The goal of the Gyro project was to assemble a mobile 3D-gyroscope integrated with a standard GPS (Global Positioning System) as a support to airborne photography of the ground. Both position, current speed, flying altitude etc. detected by the GPS and the pointing direction data obtained from the gyro system are gathered in order to map the image onto a 3-D terrain model (SVALSIM). The development of proper software tools was required to display the information on a portable PC. Attention was paid in choosing low-cost components and simple, functional design. As a result, two different systems were assembled and tested. One system for airborne carriers and one for static measurements.  Since no relative movement between target and camera are necessary for our measurements, the static system was chosen.

Figure 2. Left: The 3DM-INS. A Inertial Navigator Camera System. Right: The Govenor of Svalbard all-terrian belt mobile.  

Figure 2 shows the assembled instrument with two cameras mounted to a square frame. The 3DM Gyro and the Garmin GPS 12XL are located inside the frame. Data from these modules are written directly into each frame taken by the low resolution camera. The second camera is used to locate targets (aim the system) and to obtain high resolution images. Look at the link: http://fred.unis.no/Gyro/ for more technical  information. The whole system was operated from the roof of an all-terrain belt mobile operated by the Governor of Svalbard. The PC was located inside the vehicle.

3. SKY VIEW MEASUREMENTS
Location # 2, 3 and 4 are on the same plateau below the top of Breinosa, 520 meters above sea level. Location #2 is located 701 m south-east of the EISCAT building (#1). Location #3 is located 604 m south-south-east of the EISCAT building. Location #4 is located 602 almost due south of the EISCAT building. See the exact GPS coordinates in the images below.


Figure 3. Map of Breinosa with locations #2, #3 and #4 marked. #1 is EISCAT.

3.1 HORIZON ANGLES (SKY VIEW) BREINOSA LOCATION #2
The below images from Breinosa (location #2) are marked with date, time, longitude, latitude, altitude above sea level, speed of camera (belt mobile) and camera angles. Pitch represents elevation. Roll is horizontal deviation and yaw is direction. Note that the yaw sensor is magnetic. It is in other words just measuring the relative magnetic variation when the camera is turned, not the true heading towards north. All angles are in degrees. The images are taken turning 360 degrees starting with pointing towards the highest point of Breinosa.

Figure 4. 3DM-INS Camera images from Breinosa location #2

Note that the pitch, roll and yaw angles of the camera is measured from the center of the images (green cross). The GPS data represents the position of the 3DM-INS Camera. 

3.2 HORIZON ANGLES (SKY VIEW) BREINOSA LOCATION #3

Figure 5. 3DM-INS Camera images from Breinosa location #3

 

3.3 HORIZON ANGLES (SKY VIEW) BREINOSA LOCATION #4

Figure 6. 3DM-INS Camera images from Breinosa location #4

3.4 HORIZON ANGLES (SKY VIEW) THE AURORAL STATION IN ADVENTDALEN

Figure 7. 3DM-INS Camera images from the Auroral Station in Adventdalen.

4. LIGHT POLLUTION MEASUREMENTS
4.1 CLOUDY DAY AT THE AURORAL STATION IN ADVENTDALEN

Figure 8.
Cloudy sky conditions; Worst case Scenario of light pollution from Longyearbyen.

Some of the instruments at the station are capable of detecting light through the cloud cover. This is the case for the Silver Bullet spectrometer, which measures on the OH airglow layer located in the mesosphere (85 km up). It looks straight up. As seen from Figure 8 (A) the OH(6-2) spectrum becomes contaminated by Nitrogen emissions that originate from the street lights of Longyearbyen. Note that no stars are seen in the rather diffuse and blurry images of the cameras (panels (B) and (C) in Figure 8). The cloud layer was in this case low. This is the worst case scenario. The next figures show a clear day, ideal for low light detection.   

4.2 LIGHT POLLUTION: CLEAR DAY AT THE AURORAL STATION IN ADVENTDALEN
The below images were taken on Thursday 22:00 - 23:00 LT, 06.11.2002. The Exposure time was 30 seconds with a f-value of 2.8. The sensitivity of the CCD for the FinePix S2Pro camera from Fuijifilm corresponds to a ISO 200 standard film. The images are processed equally in brightness and contrast (histogram equalization).    


Figure 9.
Clear sky over Longyearbyen from the Auroral Station in Adventdalen. F2.8 IS0200 30 s
Archive: Dscf0151, Dscf0152, Dscf0153 & Dscf0154

Note in Fig. 9 the yellow colored sky light. It's high altitude extent is the main problem for our measurements. The distance to this source must be increased as much as possible in order to reduce the light pollution.

4.3 LIGHT POLLUTION: CLEAR DAY AT BREINOSA

Figure 10.
Clear sky over Longyearbyen from the SPEAR site, close to Breinosa. There will be less
direct light from location #4. F2.8 IS0200 30 s
Archive: Dscf0155, Dscf0156, Dscf0157, Dscf0158, Dscf0159 & Dscf0160

4.4 LIGHT POLLUTION: CLEAR DAY AT PLATÅBERGET
Figure 11.
Clear sky over Longyearbyen from Platåberget. F2.8 IS0200 30 s. Note that auroral arcs are seen through the light pollution from Longyearbyen. 
Archive: Dscf0162, Dscf0163, Dscf0164, Dscf0165, Dscf0166, Dscf0167, Dscf0168, Dscf0169
Dscf0170
, Dscf0171, Dscf0172, Dscf0173, Dscf0174 & Dscf0175.

 

5. SUMMARY
Best all sky view is obtained from Platåberget. The maximum elevation angles are due to the mountain Nordenskjold, and are only a few degrees above horizon.  On the other hand, the light pollution from Longyearbyen is a little less than the one as seen from the station. A point source approximation of the light level intensity between Platåberget and Longyearbyen, yields a factor of 0.7 times the current light intensity at the Auroral station. The town is in other words close to the site. The situation will also be worse if the airport turn on their runway lights. These are one of the strongest light sources on Svalbard. The best results with respect to light pollution was obtained from Breinosa. The town and the airport are furthest away and below instrument horizon. A point source located in Longyearbyen will deceases with a factor of 0.14 as seen from the Auroral station. Also, the difference between maximum elevation angles from the station and Breinosa is only a couple of degrees. Therefore,  the best site for a new station would be on Breinosa close to EISCAT. As for the three locations on Breinosa, it seems like location #4 is best suited, since this location will have best sky view.

 

Acknowledgement
We would like to thank Frank Johnny Olsen and Olav Tomre at the Governor of Svalbard for effective transport to Breinosa with their all-terrain belt mobile. Also, thanks to  Fred S.  Hansen at UNIS for logistics. The Auroral station in Adventdalen is owned by the University of Tromsø. The University Courses on Svalbard (UNIS) operates the station. We deeply appreciate the support of the Optical group at the Geophysical Institute, University of Alaska, who owns most of the instruments. The American program at the observatory is supported by the Atmospheric Science Division of the National Science Foundation.

References
Sigernes, F., T. Svenøe and C.S. Deehr, OPTICS at the Auroral Station in Adventdalen,  Svalbard  (78°N, 15°E), China - Norway International Symposium on Polar Science, Shanghai, China, July 2001.

Sigernes, F., T. Svenøe and C.S. Deehr, OPTICS at the Auroral Station in Adventdalen,  Svalbard  (78°N, 15°E), accepted by Chinese Journal of Polar Science, July 2002.

The 28th Annual European Meeting on Atmospheric Studies by Optical Methods (28 AM), Sigernes, F., T. Svenøe and C.S. Deehr, OPTICS at the Auroral Station in Adventdalen,  Svalbard  (78°N, 15°E), Oulu, Finland, August 2001. Accepted for publication in Proceedings of 28 AM, September 2002.

www link: http://fred.unis.no/Station/China_paper.pdf