74 research outputs found
Application of Remote Sensing for the Prediction, Monitoring, and Assessment of Hazards and Disasters that Impact Transportation
Although remote sensing has been used in predicting, monitoring, and assessing hazards and disasters for over 50 years, its use in the transportation domain is still in its infancy. This study was conducted to identify the research needs involving the use of remote sensing for such applications within the transportation domain. The first step taken was to determine the current state of remote sensing applications in the transportation domain associated with the prediction, monitor, and assessment of hazards and disasters. The second step was to identify the impacts that such events may cause and the information needed to prevent or reduce their impacts. With the knowledge of the required information, remote sensing requirements and technology limitations were defined. Then according to the knowledge of the current state of research and the limitations of remote systems, future research needs were identified. Finally, the Analytic Hierarchy Process (AHP) was used to rank these research needs
InSAR time series analysis of L-band data for understanding tropical peatland degradation and restoration
In this study, satellite radar observations are employed to reveal spatiotemporal changes in ground surface height of peatlands that have, and have not, undergone restoration in Central Kalimantan, Indonesia. Our time series analysis of 26 scenes of Advanced Land Observation Satellite-1 (ALOS-1) Phased-Array L-band Synthetic-Aperture Radar (PALSAR) images acquired between 2006 and 2010 suggests that peatland restoration was positively affected by the construction time of dams—the earlier the dam was constructed, the more significant the restoration appears. The results also suggest that the dams resulted in an increase of ground water level, which in turn stopped peat losing height. For peatland areas without restoration, the peatland continuously lost peat height by up to 7.7 cm/yr. InSAR-derived peat height changes allow the investigation of restoration effects over a wide area and can also be used to indirectly assess the relative magnitude and spatial pattern of peatland damage caused by drainage and fires. Such an assessment can provide key information for guiding future restoration activities
The applications of InSAR time series analysis for monitoring long-term surface change in peatlands
In the past three decades, peatlands all over the world such as upland bogs, tropical fens, have been undergoing significant and rapid degradations. These degradations cause carbon loss and CO2 emissions, and also fuel climate change. In this research, I present three case studies on how space geodetic tools, especially Radar Interferometry (InSAR), can be used to monitor and to advance our understanding of the long-term surface changes in peatlands.
First, I investigate the eroding extent and severity of upland UK peatlands using InSAR. Both short wavelength C-band and long wavelength L-band data are explored in this study. I detect a long-term peat subsidence rate of about 0.3 cm/yr, and 2 cm of decrease in peat height between 2002 and 2010. I also examine the coherence performance of C- and L-band over upland bogs. I find L-band data provides better coherence than C-band in upland bogs. Second, I use InSAR time series generated by L-band images to map the spatial and temporal subsidence of drained tropical peatlands in Sumatra, Indonesia. And based on InSAR-derived subsidence rate data, I estimate carbon loss or CO2 emission. Third, I assess the effectiveness of peatland restoration work in in Central Kalimantan, Indonesia using InSAR (L-band images). Restoration effects and impact factors are investigated by the spatial and temporal changes of peat height, which also provide useful information for guiding future restoration activities in this region.
Overall, this research suggests that InSAR time series is feasible to monitor long-term peat height change in peatlands, provides new insights into the dynamic surface changes in peatlands, and helps to study the carbon loss and CO2 emissions from peatlands, and understand restoration effects
Spatial and temporal statistics of SAR and InSAR observations for providing indicators of tropical forest structural changes due to forest disturbance
Tropical forests are extremely important ecosystems which play a substantial role
in the global carbon budget and are increasingly dominated by anthropogenic
disturbance through deforestation and forest degradation, contributing to emissions
of greenhouse gases to the atmosphere.
There is an urgent need for forest monitoring over extensive and inaccessible
tropical forest which can be best accomplished using spaceborne satellite data.
Currently, two key processes are extremely challenging to monitor: forest
degradation and post-disturbance re-growth.
The thesis work focuses on these key processes by considering change indicators
derived from radar remote sensing signal that arise from changes in forest structure.
The problem is tackled by exploiting spaceborne Synthetic Aperture Radar (SAR) and
Interferometric SAR (InSAR) observations, which can provide forest structural
information while simultaneously being able to collect data independently of cloud
cover, haze and daylight conditions which is a great advantage over the tropics.
The main principle of the work is that a connection can be established between
the forest structure distribution in space and signal variation (spatial statistics) within
backscatter and Digital Surface Models (DSMs) provided by SAR. In turn, forest
structure spatial characteristics and changes are used to map forest condition (intact
or degraded) or disturbance.
The innovative approach focuses on looking for textural patterns (and their
changes) in radar observations, then connecting these patterns to the forest state
through supporting evidence from expert knowledge and auxiliary remote sensing
observations (e.g. high resolution optical, aerial photography or LiDAR). These
patterns are descriptors of the forest structural characteristics in a statistical sense, but
are not estimates of physical properties, such as above-ground biomass or canopy
height. The thesis tests and develops methods using novel remote sensing technology
(e.g. single-pass spaceborne InSAR) and modern image statistical analysis methods
(wavelet-based space-scale analysis). The work is developed on an experimental basis and articulated in three test
cases, each addressing a particular observational setting, analytical method and
thematic context.
The first paper deals with textural backscatter patterns (C-band ENVISAT ASAR
and L-band ALOS PALSAR) in semi-deciduous closed forest in Cameroon. Analysis
concludes that intact forest and degraded forest (arising from selective logging) are
significantly different based on canopy structural properties when measured by
wavelet based space-scale analysis. In this case, C-band data are more effective than
longer wavelength L-band data. Such a result could be explained by the lower wave
penetration into the forest volume at shorter wavelength, with the mechanism
driving the differences between the two forest states arising from upper canopy
heterogeneity.
In the second paper, wavelet based space-scale analysis is also used to provide
information on upper canopy structure. A DSM derived from TanDEM-X acquired in
2014 was used to discriminate primary lowland Dipterocarp forest, secondary forest,
mixed-scrub and grassland in the Sungai Wain Protection Forest (East Kalimantan,
Indonesian Borneo) which was affected by the 1997/1998 El Niño Southern Oscillation
(ENSO). The Jeffries- Matusita separability of wavelet spectral measures of InSAR
DSMs between primary and secondary forest was in some cases comparable to results
achieved by high resolution LiDAR data.
The third test case introduces a temporal component, with change detection
aimed at detecting forest structure changes provided by differencing TanDEM-X
DSMs acquired at two dates separated by one year (2012-2013) in the Republic of
Congo. The method enables cancelling out the component due to terrain elevation
which is constant between the two dates, and therefore the signal related to the forest
structure change is provided. Object-based change detection successfully mapped a
gradient of forest volume loss (deforestation/forest degradation) and forest volume
gain (post-disturbance re-growth).
Results indicate that the combination of InSAR observations and wavelet based
space-scale analysis is the most promising way to measure differences in forest structure arising from forest fires. Equally, the process of forest degradation due to
shifting cultivation and post-disturbance re-growth can be best detected using
multiple InSAR observations.
From the experiments conducted, single-pass InSAR appears to be the most
promising remote sensing technology to detect forest structure changes, as it provides
three-dimensional information and with no temporal decorrelation. This type of
information is not available in optical remote sensing and only partially available
(through a 2D mapping) in SAR backscatter. It is advised that future research or
operational endeavours aimed at mapping and monitoring forest degradation/regrowth
should take advantage of the only currently available high resolution
spaceborne single-pass InSAR mission (TanDEM-X).
Moreover, the results contribute to increase knowledge related to the role of SAR
and InSAR for monitoring degraded forest and tracking the process of forest
degradation which is a priority but still highly challenging to detect. In the future the
techniques developed in the thesis work could be used to some extent to support
REDD+ initiatives
Estimation of change in forest variables using synthetic aperture radar
Large scale mapping of changes in forest variables is needed for both environmental monitoring, planning of climate actions and sustainable forest management. Remote sensing can be used in conjunction with field data to produce wall-to-wall estimates that are practically impossible to produce using traditional field surveys. Synthetic aperture radar (SAR) can observe the forest independent of sunlight, clouds, snow, or rain, providing reliable high frequency coverage. Its wavelength determines the interaction with the forest, where longer wavelengths interact with larger structures of the trees, and shorter wavelengths interact mainly with the top part of the canopy, meaning that it can be chosen to fit specific applications. This thesis contains five studies conducted on the Remningstorp test site in southern Sweden. Studies I – III predicted above ground biomass (AGB) change using long wavelength polarimetric P- (in I) and L-band (in I – III) SAR data. The differences between the bands were small in terms of prediction quality, and the HV polarization, just as for AGB state prediction, was the polarization channel most correlated with AGB change. A moisture correction for L-band data was proposed and evaluated, and it was found that certain polarimetric measures were better for predicting AGB change than all of the polarization channels together. Study IV assessed the detectability of silvicultural treatments in short wavelength TanDEM-X interferometric phase heights. In line with earlier studies, only clear cuts were unambiguously distinguishable. Study V predicted site index and stand age by fitting height development curves to time series of TanDEM-X data. Site index and age were unbiasedly predicted for untreated plots, and the RMSE would likely decrease with longer time series. When stand age was known, SI was predicted with an RMSE comparable to that of the field based measurements. In conclusion, this thesis underscores SAR data's potential for generalizable methods for estimation of forest variable changes
Understanding forest health with Remote sensing-Part II-A review of approaches and data models
Stress in forest ecosystems (FES) occurs as a result of land-use intensification, disturbances, resource limitations or unsustainable management, causing changes in forest health (FH) at various scales from the local to the global scale. Reactions to such stress depend on the phylogeny of forest species or communities and the characteristics of their impacting drivers and processes. There are many approaches to monitor indicators of FH using in-situ forest inventory and experimental studies, but they are generally limited to sample points or small areas, as well as being time- and labour-inte
The European Space Agency BIOMASS mission: Measuring forest above-ground biomass from space
The primary objective of the European Space Agency's 7th Earth Explorer mission, BIOMASS, is to determine the worldwide distribution of forest above-ground biomass (AGB) in order to reduce the major uncertainties in calculations of carbon stocks and fluxes associated with the terrestrial biosphere, including carbon fluxes associated with Land Use Change, forest degradation and forest regrowth. To meet this objective it will carry, for the first time in space, a fully polarimetric P-band synthetic aperture radar (SAR). Three main products will be provided: global maps of both AGB and forest height, with a spatial resolution of 200 m, and maps of severe forest disturbance at 50 m resolution (where “global” is to be understood as subject to Space Object tracking radar restrictions). After launch in 2022, there will be a 3-month commissioning phase, followed by a 14-month phase during which there will be global coverage by SAR tomography. In the succeeding interferometric phase, global polarimetric interferometry Pol-InSAR coverage will be achieved every 7 months up to the end of the 5-year mission. Both Pol-InSAR and TomoSAR will be used to eliminate scattering from the ground (both direct and double bounce backscatter) in forests. In dense tropical forests AGB can then be estimated from the remaining volume scattering using non-linear inversion of a backscattering model. Airborne campaigns in the tropics also indicate that AGB is highly correlated with the backscatter from around 30 m above the ground, as measured by tomography. In contrast, double bounce scattering appears to carry important information about the AGB of boreal forests, so ground cancellation may not be appropriate and the best approach for such forests remains to be finalized. Several methods to exploit these new data in carbon cycle calculations have already been demonstrated. In addition, major mutual gains will be made by combining BIOMASS data with data from other missions that will measure forest biomass, structure, height and change, including the NASA Global Ecosystem Dynamics Investigation lidar deployed on the International Space Station after its launch in December 2018, and the NASA-ISRO NISAR L- and S-band SAR, due for launch in 2022. More generally, space-based measurements of biomass are a core component of a carbon cycle observation and modelling strategy developed by the Group on Earth Observations. Secondary objectives of the mission include imaging of sub-surface geological structures in arid environments, generation of a true Digital Terrain Model without biases caused by forest cover, and measurement of glacier and icesheet velocities. In addition, the operations needed for ionospheric correction of the data will allow very sensitive estimates of ionospheric Total Electron Content and its changes along the dawn-dusk orbit of the mission
Remote sensing data acquisition, platforms and sensor requirements
Although data available from various earth observation systems have been routinely used
in many resource applications, however there have been gaps, and data needs of applications at
different levels of details have not been met. There is a growing demand for availability of data at
higher repetivity, at higher spatial resolution, in more and narrower spectral bands etc. Some of the
thrust areas of applications particularly in the Indian context are; - Management of natural resources
to ensure sustainable increase in agricultural production, - Study the state of the environment, its
monitoring and assessment of the impact of. various development actions on the environment, -
Updating and generation of large scale topographical maps. - Exploration/exploitation of marine and
mineral resources and - Operational meteorology and studying various land and oceanic processes
to understand/predict global climate changes. Each of these thrust area of application has many
components, related to basic resource areas such as agriculture, forestry, water resources, minerals,
marine resources etc. and the field of cartography. Observational requirements for major applications
have been summarized as under. Monitoring vegetation health from space remains the most
important observational parameter with applications, in agriculture, forestry, environment, hydrology
etc. Vegetation extent, quantity and temporal changes are the three main requirements which are not
fully realized with RS data available. Vegetation productivity, forest biomass, canopy moisture
status, canopy biogeochemistry are some examples. Crop production forecasting is an important
application area. Remotely sensed data has been used for identification of crops and their acreage
estimation. Fragmented holdings, large spread in crop calendars and different management practices
continue to pose a challenge lo remote sensing. Remotely sensed data at much higher spatial
resolution than hitherto available as well as at greater repetivity are required to meet this need.
Non-availability of cloud-free data in the kharif season is one of the serious problems in operational
use of remote sensing for crop inventory. Synthetic aperture radar data al X & Ku bands is
necessary to meet this demand. Nutrient stress/disease detection requires observations in narrow
spectral bands. In case of forestry applications, multispectral data at high spatial resolution of the
order of 5 to 10 metres is required to make working plans at forest compartment level. Observations
from space for deriving tree height are required for volume estimation. Observations in the middle
infrared region would greatly enhance capability of satellite remote sensing in forest fire detection.
Temporal, spatial and spectral observational requirements in various applications on vegetation
viewing are diverse, as they address processes at different spatial and time scales. Hence, it would
be worthwhile to address this issue in three broad categories. a) Full coverage, moderate spatial
resolution with high repetivity (drought, large scale deforestation, forest phenology....). b) Full
coverage, moderate to high spatial resolution and high repetivity (crop forecasting, vegetation
productivity). c) Selected viewing at high spatial resolution, moderate to high repetivity and with new
dimensions to imaging (narrow spectral bands, different viewing angles). A host of
agrometeorological parameters are needed to be measured from space for their effective use in
development of yield models. Estimation of root-zone soil moisture is an important area requiring
radar measurements from space. Surface meteorological observations from space at the desired
spatial and temporal distributions has not developed because of heavy demands placed on the
sensor as well as analytical operational models. Agrometeorology not only provides quantitative
inputs to other applications such as crop forecasting, hydrological models but also could be used
for farmer advisory services by local bodies. Mineral exploration requires information on geological
structures, geomorphology and lithology. Surface manifestation over localized regions requires large
scale mapping while the lithology can be deciphered from specific narrow bands in visible. NIR,
MIR and TIR regions. Sensors identified for mapping/cartography in conjunction with imaging
spectrometer would seem to cover requirements of this application. Narrow spectral bands in the
short regions which provide diagnostics of relevant geological phenomenon are necessary for
mineral exploration. Thermal inertia measurements help in better discrimination of different rock
units. Measurements from synthetic aperture data which would provide information on geological
structures and geomorphology are necessary for mineral exploration. The applications related to
marine environment fall in three major areas: (i) Ocean colour and productivity, biological resources;
(ii) Land-ocean interface, this includes coastal landforms, bathymetry, littoral transport processes,
etc. and; (iii) Physical oceanography, sea surface temperature, winds, wave spectra, energy and mass
exchange between atmosphere and ocean. Measurement of chlorophyll concentration accurately on
daily basis, sea surface temperature with an accuracy of 0.5 °K. and information on current
patterns arc required for developing better fishery forecast models. Improved spatial resolution data
are desirable for studying sediment and other coastal processes. Cartography is another important
application area. The major problems encountered in relation to topographic map updation are
location and geometric accuracy and information content. Two most important requirements for
such an application are high spatial resolution data of 1 to 2 metre and stereo capability to provide
vertical resolution of 1 metre. This requirement places stringent demands on the sensor
specifications, geometric processing, platform stability and automated digital cartography. The
requirements for the future earth observation systems based on different application needs can be
summarized as follows: • Moderate spatial resolution (l50-300m), high repetivity (2 Days), minimum
set of spectral bands (VIS, NIR, MIR. TIR) full coverage. • Moderate to high spatial resolution
(20-40m), high repetivity (4-6 Days), spectral bands (VIS, MR, MIR, TIR) full coverage. • High
spatial resolution (5-10m) muitispectral data with provision for selecting specific narrow bands (VIS,
N1R. MIR), viewing from different angles. • Synthetic aperture radar operating in at least two
frequencies (C, X, Ku), two incidence angles/polarizations, moderate to high spatial resolution
(20-40m), high repetivity (4-6 Days). • Very high spatial resolution (1-2m) data in panchromatic band
to provide terrain details at cadastral level (1:10,000). • Stereo capability (1-2m height resolution) to
help planning/execution of development plans. • Moderate resolution sensor operating in VIS, NIR,
MIR on a geostationary platform for observations at different sun angles necessary for the
development of canopy reflectance inversion models. • Diurnal (at least two i.e. pre-dawn and noon)
temperature measurements of the earth surface. • Ocean colour monitor with daily coverage. •
Multi-frequency microwave radiometer, scatterometer. altimeter, atmospheric sounder,
etc
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