My-linh Truong-loi - Academia.edu (original) (raw)

Uploads

Papers by My-linh Truong-loi

Apply a simple, threshold-based classifier:

2009 IEEE International Geoscience and Remote Sensing Symposium, 2009

Global warning is now known to be the major environmental issue mankind will have to face in the ... more Global warning is now known to be the major environmental issue mankind will have to face in the next decade. Monitoring of vegetation and biomass is clearly an essential piece of information required at all levels ranging from the scientific studies to understand and forecast, to the political actors and government leaders responsible for drafting remediation policies and evaluating their impact. Microwave remote sensing with the low-frequency SAR technique can provide a useful characterization of forest (spatial coverage, species, density, height…) at a global scale, relying on the all-weather imaging capabilities of SAR linked with the significant penetration of the low-frequency EM wave in the canopy. The published techniques for forest characterization from low frequency SAR data include radiometry inversion, polarimetric inversion based on the anisotropy parameters and PolInSAR Random Volume Over Ground inversion. In this paper, we will more specifically concentrate on the PolSAR technique and the impact of ionospheric effect.

IEEE Transactions on Geoscience and Remote Sensing, 2015

ABSTRACT

IGARSS 2008 - 2008 IEEE International Geoscience and Remote Sensing Symposium, 2008

1. ABSTRACT Global warning is now known to be the major environmental issue mankind will have to ... more 1. ABSTRACT Global warning is now known to be the major environmental issue mankind will have to face in the next decade. Monitoring of vegetation and biomass is clearly an essential piece of information required at all levels ranging from the scientific studies to understand and forecast, to the political actors and government leaders responsible for drafting remediation policies and evaluating their impact. Microwave remote sensing with the low-frequency SAR technique can provide a useful characterization of forest (spatial coverage, species, density, height…) at a global scale, relying on the all-weather imaging capabilities of SAR linked with the significant penetration of the low-frequency EM wave in the canopy. The published techniques for forest characterization from low frequency SAR data include radiometry inversion, polarimetric inversion based on the anisotropy parameters and PolInSAR Random Volume Over Ground inversion (1). In this paper, we will more specifically concentrate on the PolInSAR technique and the impact of ionospheric effect on this inversion. PolInSAR at low frequency can be envisioned with two radar platforms flying in formation or as a repeat pass mission. The second alternative is more plausible given the cost and the size of a low frequency SAR instrument. However the two cases will be discussed in the paper.

IGARSS 2008 - 2008 IEEE International Geoscience and Remote Sensing Symposium, 2008

In spaceborne SAR, a single-polarization on transmit has, over full polarization, the advantage o... more In spaceborne SAR, a single-polarization on transmit has, over full polarization, the advantage of a double swath due to SAR system design issues. Without getting into the details deserving by themselves a full publication, we can just observe the swath characteristics associated with ALOS PALSAR dual-pol and full-polarization modes. This increased coverage has a direct impact on the revisit time, which is always a major drive for the Earth Observing community. The options chosen up to now for current dual-pol system designs (or single-polarization on transmit) rely on a linear polarization on transmit, with two orthogonal polarizations on receive. Souyris [1] in an earlier paper proposed a more pertinent alternative for the selection of the transmit polarization leading to a better characterization of the scattering mechanisms. In a previous paper, the analysis was pursued in more depth by including the effect of the ionosphere on the wave propagation and extending the applications to polarimetric interferometry (PolInSAR). A compact pol mode was proposed where the transmit polarization is circular while the only constraint on the two receiving polarizations is independence. Both the polarimetric SAR applications and the PolInSAR applications in the context of this compact polarimetry (CP) mode were explored. A pseudo covariance matrix can be reconstructed for distributed target and was shown to be very similar to the full polarimetric (FP) covariance matrix. A PolInSAR vegetation height inversion for P Band was presented and applied to the CP data with a level of performance similar to the one associate to FP (1.2m RMS Height on the RAMSES dataset over the Landes forest). A procedure was developed to correct for the ionospheric effects for PolInSAR acquisition in FP or CP mode and the simulation on airborne data proves the procedure to be efficient and robust. In this paper, we extend the analysis of the CP mode to other sites and other datasets. For PolInSAR inversion, CP mode could be very dependant of the dominant scattering mechanisms. The double bounce effect, which is an essential element of the scattering when topography is flat, has an interesting effect on the PolInSAR behavior of forest: When the DB is present, it is usually relatively strong and focused the bottom to the trunks, lowering the overall scattering phase center. In a CP polarimetry mode, the observed polarization states are only a subset of the FP set. In the unitary circle, the complex interferometric coherences associated with a given area describe a convex region when the polarization state varies. In the hypothesis of the Random Volume Over Ground model, this region is a line and the inversion relies on the accurate estimation of this line and its intersections with the unitary circle. In a CP mode, the length of the line will therefore be shorter, potentially creating a less accurate estimate of the needed line. The previous study explored the behavior of CP on the Nezer forest which has no topography. In this study, other sites will be included where topography is present and FP PolInSAR estimation will be compared to CP PolInSAR inversion.

2011 IEEE International Geoscience and Remote Sensing Symposium, 2011

The goal of this study is to show the potential of a compactpol SAR system for vegetation applica... more The goal of this study is to show the potential of a compactpol SAR system for vegetation applications. Compact-pol concept has been suggested to minimize the system design while maximize the information and is declined as the /4, /2 and hybrid modes. In this paper, the applications such as biomass and vegetation height estimates are first presented, then, the equivalence between compact-pol data simulated from full-pol data and compact-pol data processed from raw data as such is shown. Finally, a calibration procedure using external targets is proposed.

IEEE Transactions on Geoscience and Remote Sensing, 2000

The potential of compact polarimetry (CP) mode at longer wavelengths in a space environment for s... more The potential of compact polarimetry (CP) mode at longer wavelengths in a space environment for surface parameter estimation is investigated. CP consists of transmitting a single polarization while receiving two polarizations. At longer wavelengths, one of the main challenges associated with CP from space is Faraday rotation (FR) estimation and correction. In this paper, an estimation procedure for FR is presented, which relies on the scattering properties of bare surfaces. The selection of the bare surfaces is based on a new parameter, the conformity coefficient computed from CP measurements. This parameter is shown to be FR invariant. Once estimated, the FR can be corrected over the whole image. A simple approximation to σ o HH and σ o VV based on CP measurements over bare soil surfaces is presented, from which soil moisture can be estimated using the 1995 Dubois et al. algorithm. The results obtained using CP are shown to be in good agreement with those obtained from the standard Dubois et al. algorithm using fully polarimetric data. This implies that, for soil moisture, CP can be used instead of HH and VV dual-polarized measurements.

2010 IEEE International Geoscience and Remote Sensing Symposium, 2010

Apply a simple, threshold-based classifier:

2009 IEEE International Geoscience and Remote Sensing Symposium, 2009

Global warning is now known to be the major environmental issue mankind will have to face in the ... more Global warning is now known to be the major environmental issue mankind will have to face in the next decade. Monitoring of vegetation and biomass is clearly an essential piece of information required at all levels ranging from the scientific studies to understand and forecast, to the political actors and government leaders responsible for drafting remediation policies and evaluating their impact. Microwave remote sensing with the low-frequency SAR technique can provide a useful characterization of forest (spatial coverage, species, density, height…) at a global scale, relying on the all-weather imaging capabilities of SAR linked with the significant penetration of the low-frequency EM wave in the canopy. The published techniques for forest characterization from low frequency SAR data include radiometry inversion, polarimetric inversion based on the anisotropy parameters and PolInSAR Random Volume Over Ground inversion. In this paper, we will more specifically concentrate on the PolSAR technique and the impact of ionospheric effect.

IEEE Transactions on Geoscience and Remote Sensing, 2015

ABSTRACT

IGARSS 2008 - 2008 IEEE International Geoscience and Remote Sensing Symposium, 2008

1. ABSTRACT Global warning is now known to be the major environmental issue mankind will have to ... more 1. ABSTRACT Global warning is now known to be the major environmental issue mankind will have to face in the next decade. Monitoring of vegetation and biomass is clearly an essential piece of information required at all levels ranging from the scientific studies to understand and forecast, to the political actors and government leaders responsible for drafting remediation policies and evaluating their impact. Microwave remote sensing with the low-frequency SAR technique can provide a useful characterization of forest (spatial coverage, species, density, height…) at a global scale, relying on the all-weather imaging capabilities of SAR linked with the significant penetration of the low-frequency EM wave in the canopy. The published techniques for forest characterization from low frequency SAR data include radiometry inversion, polarimetric inversion based on the anisotropy parameters and PolInSAR Random Volume Over Ground inversion (1). In this paper, we will more specifically concentrate on the PolInSAR technique and the impact of ionospheric effect on this inversion. PolInSAR at low frequency can be envisioned with two radar platforms flying in formation or as a repeat pass mission. The second alternative is more plausible given the cost and the size of a low frequency SAR instrument. However the two cases will be discussed in the paper.

IGARSS 2008 - 2008 IEEE International Geoscience and Remote Sensing Symposium, 2008

In spaceborne SAR, a single-polarization on transmit has, over full polarization, the advantage o... more In spaceborne SAR, a single-polarization on transmit has, over full polarization, the advantage of a double swath due to SAR system design issues. Without getting into the details deserving by themselves a full publication, we can just observe the swath characteristics associated with ALOS PALSAR dual-pol and full-polarization modes. This increased coverage has a direct impact on the revisit time, which is always a major drive for the Earth Observing community. The options chosen up to now for current dual-pol system designs (or single-polarization on transmit) rely on a linear polarization on transmit, with two orthogonal polarizations on receive. Souyris [1] in an earlier paper proposed a more pertinent alternative for the selection of the transmit polarization leading to a better characterization of the scattering mechanisms. In a previous paper, the analysis was pursued in more depth by including the effect of the ionosphere on the wave propagation and extending the applications to polarimetric interferometry (PolInSAR). A compact pol mode was proposed where the transmit polarization is circular while the only constraint on the two receiving polarizations is independence. Both the polarimetric SAR applications and the PolInSAR applications in the context of this compact polarimetry (CP) mode were explored. A pseudo covariance matrix can be reconstructed for distributed target and was shown to be very similar to the full polarimetric (FP) covariance matrix. A PolInSAR vegetation height inversion for P Band was presented and applied to the CP data with a level of performance similar to the one associate to FP (1.2m RMS Height on the RAMSES dataset over the Landes forest). A procedure was developed to correct for the ionospheric effects for PolInSAR acquisition in FP or CP mode and the simulation on airborne data proves the procedure to be efficient and robust. In this paper, we extend the analysis of the CP mode to other sites and other datasets. For PolInSAR inversion, CP mode could be very dependant of the dominant scattering mechanisms. The double bounce effect, which is an essential element of the scattering when topography is flat, has an interesting effect on the PolInSAR behavior of forest: When the DB is present, it is usually relatively strong and focused the bottom to the trunks, lowering the overall scattering phase center. In a CP polarimetry mode, the observed polarization states are only a subset of the FP set. In the unitary circle, the complex interferometric coherences associated with a given area describe a convex region when the polarization state varies. In the hypothesis of the Random Volume Over Ground model, this region is a line and the inversion relies on the accurate estimation of this line and its intersections with the unitary circle. In a CP mode, the length of the line will therefore be shorter, potentially creating a less accurate estimate of the needed line. The previous study explored the behavior of CP on the Nezer forest which has no topography. In this study, other sites will be included where topography is present and FP PolInSAR estimation will be compared to CP PolInSAR inversion.

2011 IEEE International Geoscience and Remote Sensing Symposium, 2011

The goal of this study is to show the potential of a compactpol SAR system for vegetation applica... more The goal of this study is to show the potential of a compactpol SAR system for vegetation applications. Compact-pol concept has been suggested to minimize the system design while maximize the information and is declined as the /4, /2 and hybrid modes. In this paper, the applications such as biomass and vegetation height estimates are first presented, then, the equivalence between compact-pol data simulated from full-pol data and compact-pol data processed from raw data as such is shown. Finally, a calibration procedure using external targets is proposed.

IEEE Transactions on Geoscience and Remote Sensing, 2000

The potential of compact polarimetry (CP) mode at longer wavelengths in a space environment for s... more The potential of compact polarimetry (CP) mode at longer wavelengths in a space environment for surface parameter estimation is investigated. CP consists of transmitting a single polarization while receiving two polarizations. At longer wavelengths, one of the main challenges associated with CP from space is Faraday rotation (FR) estimation and correction. In this paper, an estimation procedure for FR is presented, which relies on the scattering properties of bare surfaces. The selection of the bare surfaces is based on a new parameter, the conformity coefficient computed from CP measurements. This parameter is shown to be FR invariant. Once estimated, the FR can be corrected over the whole image. A simple approximation to σ o HH and σ o VV based on CP measurements over bare soil surfaces is presented, from which soil moisture can be estimated using the 1995 Dubois et al. algorithm. The results obtained using CP are shown to be in good agreement with those obtained from the standard Dubois et al. algorithm using fully polarimetric data. This implies that, for soil moisture, CP can be used instead of HH and VV dual-polarized measurements.

2010 IEEE International Geoscience and Remote Sensing Symposium, 2010