Leif Toudal Pedersen

Leif Toudal Pedersen
Technical University of Denmark | DTU · National Space Institute

PhD

About

188
Publications
23,632
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
2,164
Citations
Introduction
Leif Toudal Pedersen currently works at DTU-Space Technical University of Denmark and eolab.dk. Leif does research in Remote Sensing and modelling of sea ice and ocean. Current research projects are 'Sea Ice project of ESAs Climate Change Initiative (SICCI)', 'SST from Microwave Soundings', 'SPICES' and 'Copernicus Marine Environment Monitoring Service'
Additional affiliations
March 2017 - present
Technical University of Denmark
Position
  • Senior Researcher
Description
  • Remote sensing of ice and snow
January 2012 - February 2017
Danish Meteorological Institute
Position
  • ESA Climate Change Initiative - Sea Ice
Description
  • Production of a Climate datataset of sea ice concentration for the Northern and the Southern hemisphere after detailed evaluation of algorithms and processing methods
December 2011 - June 2016
Danish Meteorological Institute
Position
  • ICEMAR
Description
  • Developing statdards and distribution methods for data to improve safety of navigation in Polar regions
Education
August 1987 - June 1992
Technical University of Denmark
Field of study
  • Microwave Remote Sensing of Sea Ice
January 1977 - January 1982
Technical University of Denmark
Field of study
  • Electrical Engineering

Publications

Publications (188)
Poster
Full-text available
The microwave measurements of the ocean and marine cryosphere to be carried out by the Copernicus Imaging Microwave Radiometer (CIMR) satellite will contain information about a number of sea ice and snow variables. In order to better assess the potential of retrieving these variables from the future CIMR measurements we conducted a number of sensit...
Article
We report on results of an intercomparison of 10 global sea-ice concentration (SIC) data products at 12.5 to 50.0 km grid resolution from satellite passive microwave (PMW) observations. For this we use SIC estimated from >350 images acquired in the visible–near-infrared frequency range by the joint National Aeronautics and Space Administration (NAS...
Article
Full-text available
Convolutional neural networks (CNNs) are being increasingly investigated as a means to extract sea ice concentration from SAR in an automated manner. Often this is done using ice charts as training data. However, in these charts an ice concentration label is given to a large region, which may not have a spatially uniform sea ice concentration distr...
Article
Full-text available
Sea ice concentration algorithms using brightness temperatures ( T<sub>B</sub> ) from satellite microwave radiometers are used to compute sea ice concentration ( c<sub>ice</sub> ), sea ice extent, and generate sea ice climate data records (CDRs). Therefore, it is important to minimize the sensitivity of c<sub>ice</sub> estimates to geophysical nois...
Preprint
Full-text available
We report on results of an inter-comparison of 10 global sea-ice concentration (SIC) data products at 12.5 to 50.0 km grid resolution from satellite passive microwave (PMW) observations. For this we use SIC estimated from > 300 images acquired in the visible / near-infrared frequency range by joint the National Aeronautics and Space Administration...
Article
Full-text available
Owing to differing and complex snow geophysical properties, radar waves of different wavelengths undergo variable penetration through snow-covered sea ice. However, the mechanisms influencing radar altimeter backscatter from snow-covered sea ice, especially at Ka- and Ku-band frequencies, and the impact on the Ka- and Ku-band radar scattering horiz...
Article
Full-text available
Two retrieval algorithms developed as a part of the European Space Agency Climate Change Initiative (ESA-CCI) project are used to assess the effects of withholding observations from selected frequency channels on the retrieved subskin Sea Surface Temperature (SST) from AQUA's Advanced Microwave Scanning Radiometer—Earth Observing System (AMSR-E) an...
Preprint
Full-text available
This paper explores the similarities of output layers in Neural Networks (NNs) with logistic regression to explain importance of inputs by Z-scores. The network analyzed, a network for fusion of Synthetic Aperture Radar (SAR) and Microwave Radiometry (MWR) data, is applied to prediction of arctic sea ice. With the analysis the importance of MWR rel...
Article
Full-text available
Sea-ice concentration (SIC) data with fine spatial resolution and spatially continuous coverage are needed, for example, for estimating heat fluxes. Passive microwave measurements of the Advanced Scanning Microwave Radiometer 2 (AMSR2) offer spatial continuity, but are limited to spatial resolutions of 5 km and coarser. Thermal infrared data of the...
Preprint
Full-text available
Owing to differing and complex snow geophysical properties, radar waves of different wavelengths undergo variable penetration through snow-covered sea ice. However, the mechanisms influencing radar altimeter backscatter from snow-covered sea ice, especially at Ka- and Ku-band frequencies, and its impact on the Ka- and Ku-band radar scattering horiz...
Article
Full-text available
We report on results of a systematic inter-comparison of 10 global sea-ice concentration (SIC) data products at 12.5 to 50.0 km grid resolution from satellite passive microwave (PMW) observations for the Arctic during summer. The products are compared against SIC and net ice surface fraction (ISF) – SIC minus the per-grid-cell melt pond fraction (M...
Article
Full-text available
The observational uncertainty in sea ice concentration estimates from remotely sensed passive microwave brightness temperatures is a challenge for reliable climate model evaluation and initialization. To address this challenge, we introduce a new tool: the Arctic Ocean Observation Operator (ARC3O). ARC3O allows us to simulate brightness temperature...
Article
Full-text available
We explore the feasibility of an observation operator producing passive microwave brightness temperatures for sea ice at a frequency of 6.9 GHz. We investigate the influence of simplifying assumptions for the representation of sea ice vertical properties on the simulation of microwave brightness temperatures. We do so in a one-dimensional setup, us...
Article
With a growing number of different satellite sensors, data fusion offers great potential in many applications. In this work, a convolutional neural network (CNN) architecture is presented for fusing Sentinel-1 synthetic aperture radar (SAR) imagery and the Advanced Microwave Scanning Radiometer 2 (AMSR2) data. The CNN is applied to the prediction o...
Article
Full-text available
Research on improving the prediction skill of climate models requires refining the quality of observational data used for initializing and tuning the models. This is especially true in the Polar Regions where uncertainties about the interactions between sea ice, ocean and atmosphere are driving ongoing monitoring efforts. The Copernicus Imaging Mi...
Preprint
Full-text available
Abstract. We report on results of a systematic inter-comparison of 10 global sea-ice concentration (SIC) data products at 12.5 to 50.0 km grid resolution from satellite passive microwave (PMW) observations for the Arctic during summer. The products are compared against SIC and net ice-surface fraction (ISF) – SIC minus the per-grid cell melt-pond f...
Preprint
Full-text available
Abstract. The observational uncertainty in sea-ice-concentration estimates from remotely-sensed passive-microwave brightness temperatures is a challenge for reliable climate model evaluation and initialization. To address this challenge, we introduce a new tool: the Arctic Ocean Observation Operator (ARC3O). ARC3O allows us to simulate brightness t...
Preprint
Full-text available
Abstract. We explore the feasibility of an observation operator producing passive microwave brightness temperatures for sea ice at a frequency of 6.9 GHz. We investigate the influence of simplifying assumptions for the representation of sea-ice vertical properties on the simulation of microwave brightness temperatures. We do so in a one-dimensional...
Article
Full-text available
We report on results of a systematic inter-comparison of 10 global sea-ice concentration (SIC) data products at 12.5 to 50.0 km grid resolution for both the Arctic and the Antarctic. The products are compared with each other with respect to differences in SIC, sea-ice area (SIA), and sea-ice extent (SIE), and they are compared against a global wint...
Article
A statistical regression-based microwave sea surface temperature (SST) retrieval algorithm has been developed within the European Space Agency Climate Change Initiative (ESA-CCI) SST project. The retrieval algorithm was used to generate a climate data record (CDR) of passive microwave (PMW) SST from the Advanced Microwave Scanning Radiometer – Eart...
Conference Paper
ABSTRACT Today, ice charts in Greenland waters are produced manually by the Danish Meteorological Institute (DMI) for selected regions depending on season and shipping routes. The project “Automated Downstream Sea Ice Products for Greenland Waters” or shorter “Automated Sea Ice Products” (ASIP) attempts to automate this process by means of fusion o...
Article
Full-text available
Accurate sea-ice concentration (SIC) data are a pre-requisite to reliably monitor the polar sea-ice covers. Over the last four decades, many algorithms have been developed to retrieve the SIC from satellite microwave radiometry, some of them applied to generate long-term data products. We report on results of a systematic inter-comparison of ten gl...
Article
Full-text available
We introduce the OSI-450, the SICCI-25km and the SICCI-50km climate data records of gridded global sea-ice concentration. These three records are derived from passive microwave satellite data and offer three distinct advantages compared to existing records: first, all three records provide quantitative information on uncertainty and possibly applie...
Article
Full-text available
A portion of the freshwater transport through Fram Strait consists of low-salinity Pacific-derived Arctic water flowing southward along the east coast of Greenland. The pathways of this water are currently unclear. An Ice Tethered Profiler deployed over the southeastern Wandel Sea shelf (northeast Greenland) in May 2015 collected a profile every 3...
Article
We estimate the uncertainty of satellite-retrieved Arctic sea-ice thickness, sea-ice volume, and their trends stemming from the lack of reliable snow-thickness observations. To do so, we simulate a Cryosat2-type ice-thickness retrieval in an ocean-model simulation forced by atmospheric reanalysis, pretending that only freeboard is known as model ou...
Article
Full-text available
Assimilation of remote-sensing products of sea ice thickness (SIT) into sea ice–ocean models has been shown to improve the quality of sea ice forecasts. Key open questions are whether assimilation of lower-level data products such as radar freeboard (RFB) can further improve model performance and what performance gains can be achieved through joint...
Article
Full-text available
We introduce the OSI-450, the SICCI-25km and the SICCI-50km climate data records of gridded global sea-ice concentration. These three records are derived from passive microwave satellite data and offer three distinct advantages compared to existing records: First, all three records provide quantitative information on uncertainty and possibly applie...
Article
Full-text available
A new algorithm for estimating sea ice age (SIA) distribution based on the Eulerian advection scheme is presented. The advection scheme accounts for the observed divergence or convergence and freezing or melting of sea ice and predicts consequent generation or loss of new ice. The algorithm uses daily gridded sea ice drift and sea ice concentration...
Data
The RRDP sea ice concentration is a dataset of comma separated ASCII (text) files which contain reference sea ice concentrations and/or other relevant data and co-located NWP data from ERA-Interim, satellite Brightness Temperatures (TBs) extracted from the AMSR-E/AMSR2 swath datasets, ASCAT, QuikSCAT, SMOS and SMAP data to be used to for ice concen...
Article
Full-text available
The Optimal Estimation (OE) technique is developed within the European Space Agency Climate Change Initiative (ESA-CCI) to retrieve subskin Sea Surface Temperature (SST) from AQUA’s Advanced Microwave Scanning Radiometer—Earth Observing System (AMSR-E). A comprehensive matchup database with drifting buoy observations is used to develop and test the...
Technical Report
This algorithm theoretical basis document (ATBD) describes in detail the DMI OE Algorithm for the retrieval of SST from the JAXA’s Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E) instrument.
Article
Full-text available
The first-ever conductivity–temperature–depth (CTD) observations on the Wandel Sea shelf in northeastern Greenland were collected in April–May 2015. They were complemented by CTDs taken along the continental slope during the Norwegian FRAM 2014–2015 drift. The CTD profiles are used to reveal the origin of water masses and interactions with ambient...
Article
Full-text available
Assimilation of remote sensing products of sea ice thickness (SIT) into sea ice-ocean models has been shown to improve the quality of sea ice forecasts. Open questions are whether the assimilation of rawer products such as radar freeboard (RFB) can achieve yet a better performance and what performance gain can be achieved by the joint assimilation...
Article
Full-text available
In April 2015, an ice-tethered conductivity–temperature–depth (CTD) profiler and a down-looking acoustic Doppler current profiler (ADCP) were deployed from the landfast ice near the tidewater glacier terminus of the Flade Isblink Glacier in the Wandel Sea, NE Greenland. The 3-week time series showed that water dynamics and the thermohaline structur...
Presentation
Full-text available
Passive microwave satellite observations of sea ice concentrations Known issues and biases
Book
This book provides an advanced introduction to the science behind automated prediction systems, focusing on sea ice analysis and forecasting. Starting from basic principles, fundamental concepts in sea ice physics, remote sensing, numerical methods, and statistics are explained at an accessible level. Existing operational automated prediction syste...
Data
The dataset provides a Climate Data Record of Sea Ice Concentration (SIC) for the polar regions, derived from medium resolution passive microwave satellite data from the Advanced Microwave Scanning Radiometer series (AMSR-E and AMSR-2). It is processed with an algorithm using coarse resolution (6 GHz and 37 GHz) imaging channels, and has been gridd...
Article
We present experiences in using an integrated retrieval method for atmospheric and surface parameters in the Arctic using passive microwave data from the AMSR-E radiometer. The core of the method is a forward model which can ingest bulk data for seven geophysical parameters to reproduce the brightness temperatures observed by a passive microwave ra...
Article
Full-text available
In April 2015, an ice-tethered conductivity-temperature-depth (CTD) profiler and a down-looking Acoustic Doppler Current Profiler (ADCP) were deployed from the landfast ice near the tidewater glacier terminus of the Flade Isblink Glacier in the Wandel Sea, NE Greenland. The three week timeseries showed that water dynamics and the thermohaline struc...
Article
Full-text available
The first-ever conductivity–temperature–depth (CTD) observations on the Wandel Sea shelf in North Eastern Greenland were collected in April–May 2015. They were complemented by CTD profiles taken along the continental slope during the Norwegian FRAM 2014–15 drift. The CTD profiles are used to reveal the origin of water masses and interactions with a...
Conference Paper
Full-text available
The thickness of the snow layer covering sea ice is a crucial parameter in any algorithm deriving sea-ice thickness or volume from satellite-retrieved sea-ice freeboard. The assumptions on snow depth applied by these algorithms are, however, usually based on sparse observational data with large uncertainties. In this study we evaluate these assumpt...
Technical Report
Full-text available
The report is divided into 3 sections concerning sea ice temperature, concentration and displacement. The sea ice temperature monitoring is describing multi-sensor approaches to determine surface temperature profiles of the snow and ice pack, including estimation of ice surface temperature uncertainties. The sea ice displacement section describes t...
Conference Paper
Full-text available
IMBs are autonomous instruments able to continuously monitor the growth and melt of sea ice and its snow cover at a single point on an ice floe. Complementing field expeditions, remote sensing observations and modelling studies, this in-situ data is crucial to assess the mass balance and seasonal evolution of sea ice and snow in the polar oceans. E...
Article
Full-text available
An Arctic and Antarctic sea ice area and extent dataset has been generated by EUMETSAT's Ocean and Sea Ice Satellite Application Facility (OSISAF) using the record of microwave radiometer data from NASA's Nimbus 7 Scanning Multichannel Microwave radiometer (SMMR) and the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave/Image...
Article
Full-text available
Sea-ice concentrations derived from satellite microwave brightness temperatures are less accurate during summer. In the Arctic Ocean the lack of accuracy is primarily caused by melt ponds, but also by changes in the properties of snow and the sea-ice surface itself. We investigate the sensitivity of eight sea-ice concentration retrieval algorithms...
Poster
Full-text available
Changes in sea ice and iceberg conditions in and around Inglefield Bredning during the past 40 years were analyzed using high resolution optical imagery supplemented with radar satellite imagery. with the purpose of evaluating and calibrating climate-proxy reconstructions based on marine sediment core records, a 117 year fast ice time series was al...
Conference Paper
Full-text available
During phase 1 of the European Space Agency’s (ESA) climate change initiative (CCI) sea ice project (SICCI project) a sea ice concentration (SIC) data product was produced by employing a hybrid SIC retrieval algorithm comprising the Bristol and the Comiso-Bootstrap algorithm in frequency mode. SIC was computed from brightness temperatures (TB) meas...
Conference Paper
Full-text available
The next generation, post-Sentinel-1, ESA’s C-band synthetic aperture radar (SAR) system is conceived to provide simultaneously high azimuth resolution and wide swath width (HRWS). There are different ways in which the imaging capabilities of the HRWS SAR system can be exploited, which translate to different operation modes. The more attractive are...
Conference Paper
Full-text available
The first-ever conductivity-temperature-depth (CTD) observations on the Wandel Sea shelf in North Eastern Greenland were collected from the land-fast ice in April-May 2015 as a part of the Arctic Science Partnership collaboration during the first research campaign at the Villum Research Station. They were complemented by (i) the ice-tethered profil...
Article
Full-text available
An Arctic and Antarctic sea ice area and extent dataset has been generated by EUMETSAT's Ocean and Sea Ice Satellite Application Facility (OSISAF) using the record of American microwave radiometer data from Nimbus 7 Scanning Multichannel Microwave radiometer (SMMR) and the Defense Meteorological satellite Program (DMSP) Special Sensor Microwave/Ima...