Cecilie Rolstad Denby

• Gundersen, Rune; Norland, Richard & Denby, Cecilie Rolstad (2018). Geometric, Environmental and Hardware Error Sources of a Ground-Based Interferometric Real-Aperture FMCW Radar System. Remote Sensing. ISSN 2072-4292. 10(12). doi: 10.3390/rs10122070. Full text in Research Archive Show summary

  Ground-based interferometric radar systems have numerous environmental monitoring applications in geoscience. Development of a relatively simple ground-based interferometric real-aperture FMCW radar (GB-InRAR) system that can be readily deployed in field without an established set of corner reflectors will meet the present and future need for real-time monitoring of the expected increased number of geohazard events due to climate changes. Several effects affect electromagnetic waves and limit the measurement accuracy, and a careful analysis of the setup of the deployed radar system in field is essential to achieve adequate results. In this paper, we present radar measurement of a moving square trihedral corner reflector from experiments conducted in both the field and laboratory, and assess the error sources with focus on the geometry, hardware and environmental effects on interferometric and differential interferometric measurements. A theoretical model is implemented to assess deviations between theory and measurements. The main observed effects are variations in radio refractivity, multipath interference and inter-reflector interference. Measurement error due to radar hardware and the environment are analyzed, as well as how the geometry of the measurement setup affects the nominal range-cell extent. It is found that for this experiment the deviation between interferometry and differential interferometry is mainly due to variations in the radio refractivity, and temperature-induced changes in the electrical length of the microwave cables. The results show that with careful design and analysis of radar parameters and radar system geometry the measurement accuracy of a GB-InRAR system without the use of deployed corner reflectors is comparable to the accuracy of differential interferometric measurements. A GB-InRAR system can therefore be used during sudden geo-hazard events without established corner reflector infrastructure, and the results are also valid for other high-precision interferometric radar systems.

• Gundersen, Rune; Norland, Richard & Denby, Cecilie Rolstad (2018). Ground-based differential interferometric radar monitoring of unstable mountain blocks in a coastal environment. Remote Sensing. ISSN 2072-4292. 10(6). doi: 10.3390/rs10060914. Full text in Research Archive Show summary

  In this paper, we present the results of eight years of continuous monitoring with a ground-based, interferometric, real-aperture radar of two unstable mountain blocks at Tafjord on the western coast of Norway. A real-time, interferometric, ground-based radar has the capability to provide high accuracy range measurements by using the phase of the transmitted signal, thus achieving sub-millimeter accuracy when a sufficient signal-to-noise level is present. The main challenge with long term monitoring is the variations in radio refractivity caused by changes in the atmosphere. The range variations caused by refractive changes in the atmosphere are corrected using meteorological data. We use triangular corner reflectors as references to improve the signal-to-clutter ratio and improve the accuracy of the measurements. We have also shown that by using differential interferometry, a significant part of the variation caused by radio refractivity variations is removed. The overall reduction in path length variation when using differential interferometry varies from 27 to 164 times depending on the radar-to-reflector path length. The measurements reveal cyclic seasonal variations, which are coherent with air temperature. The results show that radar measurements are as accurate as data from in situ instruments like extensometers and crack meters, making it possible to monitor inaccessible areas. The total measured displacement is between 1.2 mm and 4.7 mm for the two monitored mountain blocks.

• Hulth, John; Denby, Cecilie Rolstad & Hock, Regine (2013). Estimating glacier snow accumulation from backward calculation of melt and snowline tracking. Annals of Glaciology. ISSN 0260-3055. 54(62), p. 1–7. doi: 10.3189/172756413807342965.
• Zemp, M; Thibert, E; Huss, M; Stumm, D; Denby, Cecilie Rolstad & Nuth, Christopher [Show all 16 contributors for this article] (2013). Reanalysing glacier mass balance measurement series. The Cryosphere. ISSN 1994-0416. 7(4), p. 1227–1245. doi: 10.5194/tc-7-1227-2013.
• Denby, Cecilie Rolstad (2013). Geodetiske data til bestemmelse av volumendringer av breis på Jan Mayen :. Kart og Plan. ISSN 0047-3278. 73, årg. 106(1), p. 54–63.
• Chapuis, Anne; Denby, Cecilie Rolstad & Norland, Richard (2010). Interpretation of amplitude data from a ground-based radar in combination with terrestrial photogrammetry and visual observations for calving monitoring of Kronebreen, Svalbard. Annals of Glaciology. ISSN 0260-3055. 51(55), p. 34–40. Show summary

  A ground-based radar has been used successfully for monitoring calving events and velocities at Kronebreen, Svalbard, for two test seasons in 2007 and 2008. We use daily terrestrial optical photogrammetry and continuous visual observation to validate the interpretation of a 116 hour groundbased radar amplitude of return signal data recorded from 26 to 30 August 2008. The radar was placed similar to 4 km from the glacier. It measured at high temporal rate (2 Hz) and the antenna lobe covered a width of similar to 700 m of the front. The calving-front geometry was extracted from the optical images, and its effect on radar backscatter, together with the movement of the glacier, was identified in the plot of the amplitude of the radar return signal. Calving events were detected applying an automated change-detection technique to the radar dataset. This technique allowed us to detect 92% of the events that were observed during the same time. In this paper, we focus on the method rather than on data interpretation. However, future use of this method, combined with meteorological data, tides and ocean temperature, will be valuable for calving-process studies.

• Chapuis, Anne; Denby , Cecilie Rolstad & Norland, Richard (2010). Terrestrial photogrammetry and visual observations for interpretation of ground-based interferometric radar data of the calving front of Kronebreen. Annals of Glaciology. ISSN 0260-3055.
• Hulth, John; Denby, Cecilie Rolstad; Trondsen, Karoline & Rødby, Ragnhild Wedøe (2010). Surface mass and energy balance of Sørbreen, Jan Mayen, 2008. Annals of Glaciology. ISSN 0260-3055. 51(55), p. 110–119. Show summary

  ABSTRACT. Mass-balance measurements were initiated in 2007/08 on Sørbreen, Jan Mayen, including operation of automatic weather stations in the ablation zone. Mean daily melt rate is 3.6cmw.e. d?1 for the investigated snow-free period of 115 days in June?September 2008. During this period, the net radiation is the largest contributor to melt. However, the relative contribution is highest in June (81%) and less in September (21%). The net longwave radiation is negative, acting as a heat sink. The climate on JanMayen is polar maritime with generally high humidity and overcast conditions. This leads to a positive latent heat flux, which represents condensation to the glacier surface. Persistent temperature inversions on the island lead to non-linear lapse rates and an ablation profile where melt does not necessarily decrease with increased elevation. A comparison of air temperatures on the glacier and twice-daily radiosonde ascents from the meteorological station, 20 km away from the glacier, shows that air temperatures at corresponding elevations are highly correlated (R2 = 0.94?0.96). This indicates that radiosonde temperature profiles can be valuable for determining lapse rates for melt modeling of the glacier.

• Breili, Kristian & Denby, Cecilie, Rolstad (2009). Ground-based gravimetry for measuring small spatial-scale mass changes on glaciers. Annals of Glaciology. ISSN 0260-3055. 50(50), p. 141–147.
• Rolstad, Cecilie; Haug, Torborg & Denby, Bruce (2009). Spatially integrated geodetic glacier mass balance and its uncertainty based on geostatistical analysis: application to the western Svartisen ice cap, Norway. Journal of Glaciology. ISSN 0022-1430. 55(192), p. 666–680. Show summary

  Estimates of glacier mass balance using geodetic methods can differ significantly from estimates using direct glaciological field-based measurements. To determine if such differences are real or methodological, there is a need to improve uncertainty estimates in both methods. In this paper, we focus on the uncertainty of geodetic methods and describe a geostatistical technique that takes into account the spatial correlation of the elevation differences when calculating spatially averaged elevation changes. We apply this method to the western Svartisen ice cap, Norway, using elevation differences from the surrounding bedrock derived from stereophotogrammetry. We show that the uncertainty is not only dependent on the standard error of the individual elevation differences but is also dependent on the size of the averaging area and the scale of the spatial correlation. To assess if the geostatistical analysis made over bedrock is applicable to glacier surfaces, we use concurrent photogrammetrical and laser scanning data from bedrock and a range of glacier surfaces to evaluate the dependency of the geostatistical analysis on the surface type. The estimated geodetic mass balance, and its uncertainty, is -2.6 +/- 0.9 m w.e. for the period 1968-85, and -2.0 +/- 2.2 m w.e. for 1985-2002.

• Rolstad, Cecilie (2009). Large-scale force budget: Identification if interest areas and assessment of a data set for the large drainage basin of Jutulstraumen, East Antarctica. Norsk Geografisk Tidsskrift. ISSN 0029-1951. 63(2), p. 135–144. Show summary

  A large-scale force budget is a relatively simple but useful tool for initial investigation of ice dynamics; however, it requires an extensive data set. Identification of key measurement areas and assessment of the spatial variability of the required measurement accuracies is advantageous prior to measuring such large drainage basins. Identification of areas and assessment of data requires several steps and in the paper velocities and surface topography are modelled numerically for Jutulstraumen drainage basin, representing ~1% of the Antarctic ice sheet (124,000 km2). A preliminary large-scale force budget is calculated from the modelled results, and key areas are identified. Finally, the required measurement accuracies yielding 10% uncertainty of the estimated stresses are calculated through error propagation of the force budget equations. Based on the results it is recommended to prioritize more accurate measurements for determining the driving stresses for the entire basin, and the longitudinal stresses in the funnel area of Jutulstraumen. The required measurement accuracy varies strongly over the basin, limiting the effective use of remote sensed data for deriving stresses. Radar altimetry surface elevation data can be used on the lower half of the plateau, and InSAR velocity data on the lower parts of the plateau and down-glacier.

• Haug, Torborg; Rolstad, Cecilie Eie; Elvehøy, Hallgeir; Jackson, Miriam; Maalen-Johansen, Ivar & Rolstad, Cecilie (2009). Geodetic mass balance of the western Svartisen ice cap, Norway, in the periods 1968-1985 and 1985-2002. Annals of Glaciology. ISSN 0260-3055. 50(50), p. 119–125. doi: 10.3189/172756409787769528. Show summary

  The geodetic mass balance of the Western Svartisen ice cap in northern Norway is determined in this project from photogrammetry on vertical aerial photographs taken in 1968, 1985 and 2002. The existing 1968 digital terrain model (DTM) was generated using analytical photogrammetry, and the 1985 and 2002 DTMs are newly generated using digital photogrammetry. The geodetic mass balance for the period 1968 to 1985 is -2.8 ± 0.9 m w.e., and for the period 1985 to 2002 it is -1.9 ± 1.4 m w.e. The area of the Western Svartisen decreased from 190 km2 in 1968, to 187 km2 in 1985, to 184 km2 in 2002. The outlet glacier Flatisen in the southeast retreated 1700 m during the two periods. The geodetic mass balance is also determined for Engabreen drainage basin, and the numbers are -2.1 ± 1.0 m w.e. for the first period, and -0.3 ± 1.9 m w.e. for the second. The results for Engabreen are compared to traditional mass balances, and the large deviations can not be explained from uncertainties determined for the geodetic method. The assessed errors contributing to the uncertainty in the geodetic mass balance are elevation errors, uncertainties from the applied melt correction, and the use of Sorge's law assuming constant snow thickness and density.

• Rolstad, Cecilie & Norland, Richard (2009). Ground-based interferometric radar for velocity and calving-rate measurements of the tidewater glacier at Kronebreen, Svalbard. Annals of Glaciology. ISSN 0260-3055. 50(50), p. 47–54. Show summary

  This paper presents the first attempt to measure the calving rate and flow velocity of the front of a glacier using ground-based high-range resolution interferometric radar at a high temporal rate (2 Hz). The radar, operating at 5.75 GHz, is located similar to 4 km from the calving front of Kronebreen, Svalbard. The radar measures a horizontal width of similar to 700 m of the front, and a range of 300 m. The latter includes the calving front and 250 m up-glacier. We find that the glacier surface provides permanent scatterers, so spatially continuous movements at the front and at locations further up-glacier can be tracked. For similar to 8 hours we measured a large increase in velocity at the calving front, which extended 30 m up-glacier, while further up-glacier the velocity was stable (similar to 2.5 md(-1)) during the entire period. Two large calving events were identified during this survey, removing 25 m of ice in the radar range direction normal to the ice front. The velocity of the front slowed to a stable 2.5 md(-1) after the events. During another data series the velocities were stable (similar to 2.5 md(-1)) and no calving events were identified. The method is promising for carrying out studies of processes at a calving front, as it provides spatially continuous, high-frequency accurate velocities from a safe distance to the glacier.

• Rolstad, Cecilie & Breili, Kristian (2009). Ground based gravimetry for measuring small spatial scale mass changes on glaciers. Annals of Glaciology. ISSN 0260-3055. 50(50), p. 141–147. Show summary

  Gravity change on a glacier surface is a composite of several effects, e.g. melting and accumulation of snow and ice, redistribution of mass with depth by refreezing of meltwater, and height and thickness changes of the snow and ice layers. Models and equations necessary to estimate the measured gravity change due to different effects are presented, and the propagation of observational errors is evaluated. The paper presents experiences with ground based gravity measurements carried out on Hardangerjøkulen, Norway, in spring and autumn 2007. It was found that the vertical gradient of gravity contributes most to the uncertainty in the determined mass change. With present instrumentation, the gravity can be measured with the required accuracy to determine the mass loss to ~10 % of the loss determined by conventional mass balance measurements. Finally improvements in field procedures to achieve the required accuracy for measuring the mass/density changes directly combining gravity measurements and GNSS (Global Navigation Satellite Systems) are discussed.

• Rolstad, Cecilie (2006). Spatial and temporal variations in the thermodynamics since the Last Glacial Maximum at Jutulstraumen drainage basin, East Antarctica. Norsk Geografisk Tidsskrift. ISSN 0029-1951. 60(2), p. 139–148.
• Rolstad, Cecilie & Oerlemans, Johannes (2005). The residual method for determination of the turbulent exchange coefficient applied on automatic weather station data from Iceland, Switzerland, and West Greenland. Annals of Glaciology. ISSN 0260-3055. 42, p. 367–372.
• Pälli, Anja; Moore, John & Rolstad, Cecilie (2003). Firn-ice transition zone features of four polythermal glaciers in Svalbard seen by ground-penetrating radar. Annals of Glaciology. ISSN 0260-3055. 37, p. 298–304.

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• Pail, Roland; Bingham, Rory; Braitenberg, Carla; Eicker, Annette; Floberghagen, Rune & Haagmans, Roger [Show all 12 contributors for this article] (2014). Consolidated science requirements for a next generation gravity field mission.
• Malnes, Eirik & Denby, Cecilie Rolstad (2013). Validation Of SAR Derived Wet Snow Maps At Glaciers On Jan Mayen, Norway.
• Ingunn, Burud; Moni, Christophe; Flø, Andreas Svarstad; Denby, Cecilie Rolstad & Rasse, Daniel (2013). Damage evaluation for crops exposed to a simulated leakage of geologically stored CO2 usinghyperspectral imaging technology.
• Denby, Cecilie Rolstad; Malnes, Eirik & van As, Dirk (2013). Envisat ASAR and meteorological measurments for determination of glacier snow melt on Jan Mayen.
• Denby, Cecilie Rolstad; Malnes, Eirik & van As, Dirk (2013). Envisat ASAR and meteorological measurments for determination of glacier snow melt on Jan Mayen.
• Denby, Cecilie Rolstad & Gundersen, Rune (2012). Ground based radar measurements in a marine environment for glacier calving front studies.
• Denby, Cecilie Rolstad & Hulth, John (2012). Estimating glacier snow accumulation from backward calculation of melt and snowline tracking.
• Denby, Cecilie Rolstad; Malnes, Eirik; Burud, Ingunn; Hulth, John & Hock, Regine (2012). Envisat ASAR and meteorological measurments for determination of the spatial extent of glacier snow melt on Jan Mayen, 2009.
• Denby, Cecilie Rolstad & Gundersen, Rune (2012). Ground based radar for icebeg calving measurements.
• Bentel, Katrin Irene & Denby, Cecilie Rolstad (2012). Radial Basis Functions for Regional Modelling of Gravity Changes from GRACE - a Closed Loop Simulation.
• Denby, Cecilie, Rolstad (2011). Universitetsopplæring i debattdeltagelse. Østlandets Blad.
• Denby, Cecilie, Rolstad (2011). Geomatiske metoder – isavsmelting.
• Denby, Cecilie, Rolstad (2011). Ground based interferometric radar data of Kronebreen calving front, Svalbard.
• Denby, Cecilie, Rolstad; Gundersen, Rune & Norland, Richard (2011). Ground based interferometric radar data of Kronebreen calving front, Svalbard.
• Denby, Cecilie, Rolstad; Gundersen, Rune & Chapuis, Anne (2011). Ground based interferometric radar data for calving monitoring.
• Denby, Cecilie, Rolstad (2011). Glaciology at Svalbard and Jan Mayen.
• Denby, Cecilie, Rolstad & Hulth, John (2011). Assessment of differentiated surface elevation data from 1949, 1975 and 2008 for estimates of ice-volume changes at Jan Mayen. Journal of Glaciology. ISSN 0022-1430. 57(205), p. 976–980.
• Chapuis, Anne; Rolstad, Cecilie & Norland, Richard (2010). Experiences with the use of ground based interferometric radar near the calving front of Kronebreen, Svalbard. (Invited).
• Chapuis, Anne; Rolstad, Cecilie & Norland, Richard (2009). Ground based interferometric radar for velocity and calving rate measurements of the tidewater glacier Kronebreen, Svalbard, from August 2007 and 2008.
• Hulth, John; Rolstad, Cecilie & Hock, Regine (2009). Radiosonde data for temperature lapse rates and radiation transmissivity indexs in a distributed temperature-index melt model of Sørbreen, Jan Mayen.
• Rolstad, Cecilie & Hulth, John (2009). The direct glaciological mass- and energy balance of Sørbreen, Jan Mayen, for the ablation season 2008.
• Rolstad, Cecilie & Chapuis, Anne (2009). What can we see on a radar return signal from a calving front?
• Rolstad, Cecilie & Chapuis, Anne (2009). Calving processes of Kronebreen, Svalbard: calving rate variations and their possible controls.
• Gjevestad, Jon Glenn; Chapuis, Anne & Rolstad, Cecilie (2009). Isen skjelver.
• Rolstad, Cecilie & Norland, Richard (2009). Ground based interferometric radar for velocity and calving rate measurements of the tidewater glacier Kronebreen, Svalbard, from August 2007 and 2008.
• Rolstad, Cecilie; Haug, Torborg & Denby, Bruce (2009). Geodetic glacier mass balance and its uncertainty based on a spatial statistical analysis: application to the Western Svartisen ice cap, Norway.
• Chapuis, Anne & Rolstad, Cecilie (2009). Investigating the calving rate variations of Kronebreen, Svalbard, using terrestrial photogrammetry and direct observations.
• Chapuis, Anne; Rolstad, Cecilie & Norland, Richard (2009). Electromagnetic interference in ground-based interferometric radar data from Kronebreen (Svalbard) calving front due to multipath scattering and tidal cycles. Journal of Glaciology. ISSN 0022-1430. p. 943–945.
• Rolstad, Cecilie (2009). Geofaglig verktøykasse.
• Chapuis, Anne & Rolstad, Cecilie (2008). Calving dynamics of Kronebreen.
• Chapuis, Anne & Rolstad, Cecilie (2008). Terrestrial photogrammetry for measurement of the calving rate of Kronebreen, Svalbard.
• Chapuis, Anne; Maalen-Johansen, Ivar & Rolstad, Cecilie (2008). Terrerstrial photogrammetry for measurements of the calving rate of Kronebreen, Svalbard.
• Chapuis, Anne; Maalen-Johansen, Ivar & Rolstad, Cecilie (2008). Terrerstrial photogrammetry for measurements of the calving rate of Kronebreen, Svalbard.
• Rolstad, Cecilie; Haug, Torborg; Maalen-Johansen, Ivar & Jackson, Miriam (2008). Geodetic mass balance of the western Svartisen ice cap in the period 1968 to 2002. Show summary

  The geodetic mass balance of the Western Svartisen ice cap in northern Norway is determined in this project from photogrammetry on vertical aerial photographs taken in 1968, 1985 and 2002. The existing 1968 digital terrain model (DTM) was generated using analytical photogrammetry, and the 1985 and 2002 DTMs are newly generated using digital photogrammetry. The geodetic mass balance for the period 1968 to 1985 is -2.8 ± 0.9 m w.e., and for the period 1985 to 2002 it is -1.9 ± 1.4 m w.e. The area of the Western Svartisen decreased from 190 km2 in 1968, to 187 km2 in 1985, to 184 km2 in 2002. The outlet glacier Flatisen in the southeast retreated 1700 m during the two periods. The geodetic mass balance is also determined for Engabreen drainage basin, and the numbers are -2.1 ± 1.0 m w.e. for the first period, and -0.3 ± 1.9 m w.e. for the second. The results for Engabreen are compared to traditional mass balances, and the large deviations can not be explained from uncertainties determined for the geodetic method. The assessed errors contributing to the uncertainty in the geodetic mass balance are elevation errors, uncertainties from the applied melt correction, and the use of Sorge's law assuming constant snow thickness and density.

• Rolstad, Cecilie & Norland, Richard (2008). Ground based interferometric radar for velocity and calving rate measurements of the tidewater glacier Kronebreen, Svalbard. Show summary

  We here present the first attempt to measure the calving rate and the flow velocity of the front of a glacier using ground based high range resolution interferometric radar at a high temporal rate (2 Hz). The radar, operating at 5.75 GHz, is located approximately 4 km from the calving front of Kronebreen. The radar measures a horizontal width of ~700 m of the front, and a range of 300 m. The latter includes the calving front and 250 m up-glacier. We find that the glacier surface provides permanent scatterers, so spatially continuous movements at the front and at locations further up-glacier can be tracked. For ~8 hours we measure a large increase in velocity at the calving front and extending 30 m up-glacier, while further up-glacier the velocity is stable (~2.5 md-1) during the entire period. Two large calving events are identified during this ~8 h survey, removing 25 m of ice in the radar range direction normal to the ice front. The velocity of the front slows to a stable 2.5 md-1 after the events. During another data series the velocities are stable (~2.5 md-1) and no calving events are identified. The method is promising for carrying out studies of processes at a calving front, as it provides spatially continuous, high frequency accurate velocities from a safe distance to the glacier.

• Rolstad, Cecilie & Breili, Kristian (2008). Ground based gravimetry and GPS for measuring small scale mass changes on glaciers. Show summary

  The gravity field at the Earth's surface is determined by its own internal distribution of masses, by the mass distribution at or near the surface, and by other nearby moving masses such as the sun, moon and planets. The principal sources of gravity variation are tides, hydrology, postglacial rebound, land subsidence, ocean tide loading, atmospheric loading, and changes in the Earth's cryosphere. The aim of this study is to evaluate the use of gravimetric measurements for determining the local mass balance of glaciers. As such we describe a simple gravitational model of a glacier and its surface mass balance, and review the propagation of measurement errors through this model. To gain practical experience in carrying out the required gravimetric measurements in order to implement this model, a field experiment was carried out on Hardangerj\o{}kulen in Norway during the spring and autumn of 2007. The results are compared to GPS measurements, carried out as part of the study. It is found that the measured gravity change is dominated by the vertical gradient of gravity, rather than the actual change in mass of the glacier.

• Rolstad, Cecilie (2006). Geomatikk og Galsiologi.
• Rolstad, Cecilie & Oerlemans, Johannes (2006). Updating North Atlantic glacier length records from optical satellite images.
• Rolstad, Cecilie & Oerlemans, Johannes (2006). Updating North Atlantic glacier length records from optical satellite images.
• Maalen-Johansen, Ivar; Hegstad, Einar; Sevatdal, Hans; Steinsholt, Håvard; Øvstedal, Ola & Rolstad, Cecilie (2006). Utdanning av eiendomslandmålere ved UMB. Kart og Plan. ISSN 0047-3278. 66(1), p. 39–45. Show summary

  A major issue in the new legislation on land registration, passed in the Parliament spring 2005, and hopefully taking effect in 2007, is the need to improve the qualifications of the surveying profession. The response, in terms of policy for revision of study programs at the Norwegian University of Life Sciences, are presented an discussed in the article. Solutions for improved curriculum in the relevant master programs, as well as upgrading programs for professionals, are outlined.

• Rolstad, Cecilie & Oerlemans, Johannes (2004). The residual method for determination of the turbulent exchange coefficient applied on automatic weather station data from Iceland, Switzerland, and West Greenland.
• Smedsrud, Lars Henrik & Rolstad, Cecilie (2002). Mindre is i et varmere Antarktis. Cicerone. ISSN 0804-0508. 11(3), p. 32–35.

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