Bakgrunn og aktiviteter

Hossein Nahavandchi er professor i geodesi og geofysikk. Hans forskningsinteresser er klimaendringer/overvåking av jorden ved hjelp av satellittdata.

Biography:  Hossein Nahavandchi holds a PhD degree (1998) from Royal Institute of Technology in Stockholm. His primary research interest is satellite Gravimetry, Altimetry and GPS. He has been lecturing in the Geomatics and Geodesy fields since 1990. Hossein’s career includes being a member of staff at Isfahan University (as Senior Lecturer and Head of Department), Royal Institute of Technology in Stockholm (as Research Associate), Tehran University (as Assistant Professor), and Norwegian University of Science and Technology (as Associate Professor and Professor). He also worked for Iranian National Mapping Authority and National Cartographic Center (NCC)  in several functions. He has been the Rector of the College of NCC, Division Director, Chair of the Borad and Board member of Research and Planning Division, and Education Department in Iran. His research projects and activities in Civil Engineering  (BOA activities) have attracted more than 100 million NOK to the university sector since 1991. They have also resulted in a strong international network. Over 155 publications and presentations are the results of his research projects.  

Mine forskningsområder

Nåværende forskning: Ocean wave measurments using single GPS Buoy 

Accurate forecasts of wave conditions are of the utmost important to all who live, work, or travel on or near ocean. To improve the wave prediction models, field measurement of ocean wave parameters is necessary. Those parameters are wave height, period and direction. We applied a methodology to derive ocean wave parameters (wave height, wave period and direction) from GPS data. The power spectrums of GPS data (among its errors) and buoy movement (excited by ocean wave) were the basis for the estimation of wave parameters. Because of the buoy movement data is in the band frequency of GPS data which signal to noise ratio (SNR) is very low, the most important point in design of high pass filter is the cut-off frequency selection of the filter. The figure below shows the power spectrum of the GPS height data in m2/Hz.  

  

   

Nåværende forskning: Greenland Ice-mass balance from satellite gravity observations 

The Gravity Recovery and Climate Experiment (GRACE) satellite mission provides temporal variations of Earth gravity field with a period of around one month. GRACE measures changes in Earth's gravity field caused by regional shifts in the Earth's mass, including ice sheets, oceans and Water stored in the soil and in underground aquifers. We used GRACE data to estimate the rate of ice mass variability over Greenland. The Figure below shows monthly ice mass changes summed over the entire Greenland ice sheet, between April 2002 and February 2010, estimated in Gigatonne grom three GRACE data sets released by GFZ (Potsdam), JPL(California) and CSR (Texas). Note that this plot shows deviation from the average ice mass over the 2002 to 2010 period. It does not mean that the ice sheet was gaining ice before 2006 but that ice mass was over the 2002 to 2010 average. The ice mass was below the 2002 to 2010 average after 2006. The trend of the best fitting straight line for CSR data is -163±20 Gigatonne per year. The results also indicate the the ice-mass loss rate has been increasing in the time period between 2002 and 2010.  

 

In another experiment we calculated the resulting secular trends in Greenland ice mass in two different periods. Figures below show the secular trends in the greenland ice mass variability represented as the equivalent water avergaed between April 2002 and December 2007 (figure in the left), and between April 2002 and December 2010 (Figure in the right). These two figures illustrate where Greenland lost mass faster during the study period. It is shown that the well documented Greenland ice mass loss in the southern region is now spread to northwest Greenland in the period between 2007 and 2010.

Nåværende forskning: Ocean circulation in North Atlantic and the Arctic sea from satellite altimetry observations

The Ocean plays a key role in determining the global climate. To develop techniques for pridicting furure climate, one must undrestand the dynamics of the global ocean circulation. A viable approach to observing the global and regional ocean circulations with sufficient resolution is the use of a satellite radar altimeter to measure the Mean Sea Surface (MSS) height. Multiple radar altimetry data from ESA satellites of ENVISAT, ERS-1 and ERS-2 and NASA satellite of GFO were used to determine the NTNU MSS model. NTNU MSS model is used to derive the mean dynamic topography and the ocean circulation as it is shown in the Figure below. This plot shows the surface current system in the North Atlantic and the Arctic sea for the time period 1993-2007. Flow of warm water is shown as red arrow and cold water as blue arrow. The northward flow of warm water in the North Atlantic is partly balanced by soutward flow of cold water in the East Greenland. Note that the detalied arrows for the surface currents are not shown in this picture. 

 

Forskning (nøkkelord)

  • Satellitttposisjonering GPS
  • Satellittgravimetri og altimetri
  • Klimaforandring
  • Polarforskning
  • Havsirkulasjon og havnivåheving
  • Havbølge målinger

Forskningstema

  • Arctic (Greenland) and Antarctic Mass balance (Ice loss, resulting sea level rise) from satellite gravity and satellite altimetry mesaurements 
  • Ocean Circulation and Transport Between the North Atlantic and Arctic sea (OCTAS)
  • New improvments in Geoidal height modeling
  • Development of a regional GPS-based model of Ionospheric VTEC for Norway
  • Arctic geoid for ocean circulation, sea-ice exploration and climate change 

Mine Undervisning

  • TBA4852 Eksperter i team (EiT)
  • TBA4565 Geomatikk, fordyningsemne
  • TBA4560 Geomatikk, fordyningsprosjekt
  • TBA4567 Fysikalsk geodesi
  • TBA4565 Geometrisk sattelittgeodesi (GPS)
  • TTT4234 Romteknologi I
  • TBA4925 Geomatikk, Masteroppgave
  • BA8200 Videregående feilteori og utjevningsregning
  • BA8202 Videregående fysikalsk geodesi
  • BA8604 Satellitt-gravimetri og -altimetri
  • BA8605 Videregående global satellitt-posisjonering GPS
  • BA8203 En integrert jordbasert metode for studium av havklima

Lenker:

 

 

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