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| 2. |
- Blixt, E. M., et al.
(författare)
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Optical flow analysis of the aurora borealis
- 2006
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Ingår i: IEEE Geoscience and Remote Sensing Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1545-598X .- 1558-0571. ; 3:1, s. 159-163
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Tidskriftsartikel (refereegranskat)abstract
- Optical observations of the aurora have traditionally focused on the structure, intensity, and wavelength of the emissions. But the apparent motion of auroral forms offers another important diagnostic tool for investigating this poorly understood phenomenon. Prior analyses of auroral motion have focused on tracing individual features. In this letter, we investigate the feasibility of deriving the entire two-dimensional velocity field automatically using robust optical flow estimation. The analysis is applied to two narrow-field video sequences. Both examples are rich in small-scale structure and motion, but appear very different to the eye. The robust optical flow estimator performed well for regions of dense turbulent motion, while sheared flow and flow which is perpendicular to image intensity gradients, was poorly resolved. The relative magnitude of the outliers provides a quantitative measure of the validity of the underlying flow model and, hence, a means of automatically differentiating among auroral forms with differing physical origins. The technique can be used to deduce ionospheric electric fields and neutral winds, and the flow fields yield important physical information about the generation mechanism.
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| 3. |
- John, Viju Oommen, et al.
(författare)
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A cautionary note on the use of Gaussian statistics in satellite-based UTH climatologies
- 2006
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Ingår i: IEEE Geoscience and Remote Sensing Letters. - 1545-598X .- 1558-0571. ; 3:1, s. 130-134
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Tidskriftsartikel (refereegranskat)abstract
- This letter presents a cautionary note on the assumption of Gaussian behavior for upper tropospheric humidity (UTH) derived from satellite data in climatological studies, which can introduce a wet bias in the climatology. An example study using European Centre for Medium-Range Weather Forecasts reanalysis data shows that this wet bias can reach up to 6 %RH, which is significant for climatological applications. A simple Monte Carlo approach demonstrates that these differences and their link to the variability of brightness temperatures are due to a log-normal distribution of the UTH. This problem can be solved by using robust estimators such as the median instead of the arithmetic mean.
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| 4. |
- Sandberg, Gustaf, 1982, et al.
(författare)
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Measurements of Faraday Rotation Using Polarimetric PALSAR Images
- 2009
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Ingår i: IEEE Geoscience and Remote Sensing Letters. - 1558-0571 .- 1545-598X. ; 6:1, s. 142-146
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Tidskriftsartikel (refereegranskat)abstract
- For spaceborne synthetic aperture radar (SAR) systemsoperating at L-band frequencies or lower, the ionospheremay have a significant impact on the SAR images. The largesteffect at L-band is caused by Faraday rotation (FR). Severalstudies have modeled the effect of FR and/or devised models to measure and correct FR.With the launch of the fully polarimetric L-band system Phased Array-type L-band SAR (PALSAR), it has become possible to test both models and measurement techniques on real SAR data. In this letter, the quality of calibrated polarimetric PALSAR data is assessed, and FR is measured. It is found that residual crosstalk and channel imbalance are small in the PALSAR data. Two methods are used to measure FR, the first using in-scene distributed targets and the second using large trihedrals. The two methods show very good agreement. The measurements are compared with values of the total electron content using a linear model. It is found that the model and measurements are in good agreement, with a root-mean-square error of 0.3◦ or 15% of the mean FR angle.
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| 5. |
- Somasundaram, Samuel D., et al.
(författare)
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Countering Radio Frequency Interference in Single Sensor Quadrupole Resonance
- 2009
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Ingår i: IEEE Geoscience and Remote Sensing Letters. - 1545-598X. ; 6:1, s. 62-66
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Tidskriftsartikel (refereegranskat)abstract
- Nuclear quadrupole resonance (NQR) is a solid-state radio frequency (RF) spectroscopic technique that allows for the detection of many narcotics and highly explosive substances. Unfortunately, the practical use of NQR is often restricted by the presence of strong RF interference (RFI). In this letter, extending our recent work on stochastic NQR (sNQR), we propose acquiring signal-of-interest free samples, containing only corrupting signals, and exploiting them to reduce the effects of RFI on conventional NQR (cNQR) measurements. Similar to the sNQR case, the presented detectors are able to substantially outperform previous cNQR detectors when RFI is present.
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