Institutt for fysikk og teknologi

Air temperature at 90 km altitude in the Artic obtained using meteor radar : validation, characterization and climate change.

Kluken, Lars Grytbakk — 2011-09-29T22:00:00Z

Kluken, Lars Grytbakk
Temperatures at 90 km altitude above Ramfjordmoen (69°N, 19°E) have been obtained with the Nippon/Norwegian Tromsø Meteor Radar. The temperatures have been derived from meteor radar decay rates using two techniques: the pressure based and the temperature gradient based methods. The results have been compared to the Microwave Limb Sounder (MLS) instrument on board the Aura spacecraft. It was found that the pressure method was simpler to implement than the temperature gradient method and gave better results in relation to the MLS temperatures. With the use of a technique for statistical comparison of geophysical data, the intrinsic uncertainty of the radar temperatures was estimated to be less than 4 K. Two attempts to combine the two techniques in order to measure both temperatures and pressure with the meteor radar have been carried out. One of the approaches proved to be feasible and gave promising results. This indicates that the meteor radar may have the potential of producing continuous temperature and pressure measurements virtually independent of external data. A new collocated sodium lidar is introduced and some initial comparisons are carried out between the two instruments. At times there were large discrepancies, but more data is necessary in order to obtain reliable results. Finally, some possible uses of the radar temperatures are proposed. A method for investigating long term trends is discussed in detail. The data available resulted in a trend of - 2.2 K per decade, but more data is required to establish a trend with higher confidence. It was estimated that approximately 13 years of data are needed to determine the trend with a probability of 90 %.

A K-Wishart Markov random field model for clustering of polarimetric SAR imagery

Moser, Gabriele — 2010-12-31T23:00:00Z

Moser, Gabriele; Akbari, Vahid; Eltoft, Torbjørn; Doulgeris, Anthony Paul; Anfinsen, Stian Normann; Sebastian, Serpico

On the measurement of subsonic flow in a capacitively coupled helicon plasma source

Fredriksen, Åshild — 2009-12-31T23:00:00Z

Fredriksen, Åshild; Mishra, Lekha Nath; Gulbrandsen, Njål; Miloch, Wojciech Jacek
Plasma parameters and the subsonic flow from a capacitively coupled, cylindrical plasma source of the Njord helicon device are investigated by means of a Mach probe and a retarding field energy analyzer (RFEA). 13.56 MHz and 600 W RF power is inserted into the argon working gas under low-pressure conditions and moderate magnetic field. By means of a downstream field coil, the magnetic field is shaped from a purely expanding field to a configuration with more parallel field lines. It is shown that the downstream plasma density along the outer rim of the source increases significantly and there is a sudden increase by nearly 20 V in the plasma potential already after a moderate increase in the downstream magnetic field. The investigation of the flow indicates that current ratios derived from the Mach probe result in an apparent flow in the direction towards the source, while the current bratios derived from the RFEA indicate a flow in the direction away from the source. PIC simulations demonstrate that the acceptance angle of the probes, being nearly 180o for the Mach probe, and about 45o for the RFEA, can critically affect the current ratios and hence the subsonic flow measured by the probes in the weakly magnetized plasma in our device. The first section in your paper

Fotoelektriske observasjonar av stjerneokkultasjonar ved måneranda

Høydalsvik, Stein — 1979-12-31T23:00:00Z

Høydalsvik, Stein
Analyser av okkultasjonskurvene frå fotoelektriske observasjonar viser at ein stor del av dei observerte stjernene er dobbelstjerner. Okkultasjonsteknikken kan lett åtskilje stjerner som har ein vinkelavstand større enn 0",01 og under gunstige tilhøve kan oppløysinga vere 0",001. I tillegg kan analysen av observasjonen gje vinkeldiameteren til stjerna dersom han er større enn 0",001. Utfrå vinkeldiameteren kan vi bestemme den effektive temperaturen som er ein fundamental storleik for ei stjerne. Ved observasjonar av okkultasjonar kan vi såleis få verdifull informasjon om stjernene som vert okkultert. Eg har valt å konsentrere meg om den okkulterte stjerna og kva informasjon ein analyse av okkultasjonskurva kan gje om ho. Ein vesentleg del av arbeidet har vore å prøve ut observasjonsutstyret i Skibotn på slike observasjonar og eventuelt kome med forslag om forbetringar av dette. Eit viktig siktemål med dette arbeidet var å tilretteleggje ei enkel observasjonsprosedyre slik at ein seinare kan observere okkultasjonar utan stor arbeidsinnsats, nærmast som ein rutineobservasjon. I kapittel 2, 3 og 4 viser eg korleis vi kan bruke generell diffraksjonsteori i tolkinga av ei okkultasjonskurve. Eg diskuterer også mogelege feilkjelder i denne tolkinga. Kapittel 5 viser instrumentasjonen som vart brukt til observasjonane og gjev ei prosedyre for slike observasjonar. Kapittel 6 forklarar kort analyseprogrammet, og eg diskuterer mogelege forbetringar av det. Kapittel 7 presenterer dei einskilde observasjonane og analyseresultata av dei. Eg gjev ei vurdering av kor gyldige desse resultata er. Kapittel 8 er så ein diskusjon av observasjonskvaliteten og kva innverknad ulike faktorar har på denne. Særleg ser eg på kva innverknad scintillasjonen kan ha. Til slutt gjev eg så i kapittel 9 ei oppsummering av dei viktigaste resultata samt ei vurdering av kva rolle okkultasjonsobservasjonar kan/bør ha ved observatoriet i Skibotn i framtida.
Dette er ei hovudfagsoppgåve

Trapping of Nanoparticles with Optical Waveguides

Dullo, Firehun Tsige — 2011-05-17T22:00:00Z

Dullo, Firehun Tsige
Over the last few years, the notion that links optical trapping with strong intensity of light (high energy photon) not only forced the modification of optical tweezer, but it also open up the door for evanescent wave field trapping. While optical tweezer is merely suitable for trapping micro-sized particles, trapping by evanescent field of a channel waveguide enables both micro and nanosized particles to be trapped and propel as well. Indeed, nowadays, various structures of channel wave guides are designed to secure higher intensity of light for significantly better trapping purposes. The goal of this study is mainly to examine and better understand features related to trapping of particles on three different structures of a waveguides: straight, loop and ring resonators. We also propose new method to characterize the ring resonator waveguide. Though there are limitations to this method, it is possible to measure power in and out of the ring. Besides, the characteristics result shows too much power loss. From the straight waveguide experiment we confirm that gold particles of diameter 200nm and 500nm are trapped and propelled above the waveguide by the evanescent field. The speed obtained from the 200nm diameter analysis reaches up to 420µm/s for 700mW laser power, which considerably faster than the previously reported values. Given the advantages of the applications of loop waveguides, to stop particles by standing waves or counter propagating beams, we are able to clearly observe this phenomenon in our experiment for 1.02µm diameter polyester particles, in contrast to gold nanoparticles due to weak gradient forces. Maintaining similar analysis for ring resonator waveguides, however, the lacking of particle trapping or propulsion is observed for gallium arsenide nanowires, due to their asymmetric structure besides the low power. Weak gradient force and low power in the gold, and low power though strong gradient force in polystyrene ring waveguides are responsible for lack of trapping and propulsion in the nanoparticles. Even though the priority is of this thesis is the experimental essence, the theories of optical waveguides and optical trapping forces are briefly reviewed.

Particle precipitation during NEIAL events : simultaneous ground based nighttime observations at Svalbard

Lunde, June — 2008-12-31T23:00:00Z

Lunde, June; Løvhaug, Unni Pia; Gustavsson, Björn Johan

Na lidar measurements during the ECOMA/Geminids campaign with focus on Na peak density and temperature

Østerpart, Jørgen Olai Kristensen — 2011-01-31T23:00:00Z

Østerpart, Jørgen Olai Kristensen
Using a resonance lidar, atomic Na (sodium) can be observed in the 80-110 km altitude range of the atmosphere. Na belongs to the alkali metal group and is highly reactive, so one could expect that it would quickly react with other particles and leave its atomic state. Its actual behaviour however includes the formation of relatively dense layers which, from the perspective of a stationary lidar, form suddenly and can last for several hours before quickly disappearing again. Several theories on the formation of these layers have been developed, including temperature dependent chemical processes, but none of them seem to explain all of the observed events. In 2008, two articles about these sudden sodium layers were published by scientists who have worked with the Weber Na lidar at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR), located at Andøya, Norway \((69^{\circ} 16' N, 16^{\circ} 00' E)\). Nesse et al. (2008) describe one particular Na layer observed 5 November 2005 and consider in turn how the most probable theories match the observed data during this event. Heinrich et al. (2008) identify all the sudden Na layers that have been observed on ALOMAR between August 2000 and June 2006 and investigate in particular how these coincide with sporadic E-layers (thin layers of several types of metallic ions). The fourth ECOMA (Existence and Charged State of Meteoric Smoke Particles in the Middle Atmosphere) rocket campaign took place at the Andøya Rocket Range during November and December 2010. The Na lidar was operated to the extent possible during this period, resulting in near real-time data for two of the three rocket launches and a total of 48 hours of measurements which are presented in this text. Using the two formerly mentioned articles as a starting point, I have studied available theory about sudden Na layers and the ALOMAR Na lidar in particular, and the upper atmosphere and resonance lidars in general. While we did not observe any sudden Na layers during the ECOMA measurements, I look into an older dataset as an example.

On the secondary charging effects and structure of mesospheric dust particles impacting on rocket probes

Havnes, Ove — 2006-12-31T23:00:00Z

Havnes, Ove; Næsheim, Lars Irgens

Remote Oxygen Sensing by Ionospheric Excitation (ROSIE)

Kalogerakis, K. S. — 2008-12-31T23:00:00Z

Kalogerakis, K. S.; Gustavsson, Björn Johan; Slanger, T. G.; Rietveld, Michael T; Kendall, E. A.; Pedersen, T. R.; Kosch, M. J.

First estimates of volume distribution of HF-pump enhanced emissions at 6300 and 5577 Å : a comparison between observations and theory

Kosch, Mike — 2007-12-31T23:00:00Z

Kosch, Mike; Gustavsson, Björn Johan; Wong, Alfred; Pedersen, Todd; Heinselman, Craig; Mutiso, Charles; Bristow, Bill; Hughes, John; Wang, Weiyuan
We present bi-static observations of radio-wave induced optical emissions at 6300 and 5577 Å from a night-time radio-induced optical emission ionospheric pumping experiment at the HIPAS (Fairbanks) facility in Alaska. The optical observations were made at HIPAS and from HAARP located 285 km south-east. From these observations the altitude distribution of the emissions is estimated with tomography-like methods. These estimates are compared with theoretical models. Other diagnostics used to support the theoretical calculations include the new Poker Flat AMISR UHF radar near HIPAS. We find that the altitude distribution of the emissions agree with electron transport modeling with a source of accelerated electrons located 20 km below the upper-hybrid altitude.