The document discusses Digital Terrain Model (DTM) generation using interferometry, focusing on the techniques and challenges of synthetic aperture radar (InSAR) for generating accurate elevation data. It outlines the importance of phase measurement accuracy, imaging geometry, and wave propagation conditions in determining DTM accuracy, while also addressing potential errors from system noise and atmospheric influences. Various methodologies for calculating phase differences and converting these to elevation values are explored, along with strategies for error assessment in DTM creation.

1. DTM
Generation
Using
Interferometery

2. Interferometery
Interferometery
•
The location and examination of sources of
The location and examination of sources of
electromagnetic radiation through the
electromagnetic radiation through the
simultaneous use of two or more separated
simultaneous use of two or more separated
telescopes
telescopes.
. Interferometers produce
Interferometers produce
overlapping wave patterns from the
overlapping wave patterns from the
radiation
radiation.
. These patterns are studied to
These patterns are studied to
determine the brightness and angular
determine the brightness and angular
structure of the emitting source
structure of the emitting source
.
.

3. Commonly used wavelengths
Commonly used wavelengths
•
X_band(3cm)
X_band(3cm)
•
C_band(5cm)
C_band(5cm)
•
L_band(25cm)
L_band(25cm)

4. abstract
abstract
•
synthetic aperture radar (InSAR) is a rapidly
synthetic aperture radar (InSAR) is a rapidly
evolving technology for DTM generation. It
evolving technology for DTM generation. It
exploits the coherent nature of SAR imaging
exploits the coherent nature of SAR imaging
to measure Interferometric stereo parallaxes
to measure Interferometric stereo parallaxes
in the mm and cm regime from phase
in the mm and cm regime from phase
differences
differences
.
.

5. SAR (InSAR)
SAR (InSAR) INTERFEROMETRY
INTERFEROMETRY

6. The flow of the process

7. Stereo Radar
Stereo Radar

8. •
Geometric Corresponding
Geometric Corresponding
Geometric correction were carried out
Geometric correction were carried out
for corresponding to two SAR images
for corresponding to two SAR images.
.
Calculation of the phase difference
sabtracted the phase of SAR1 from one of
SAR2
Calculation of the orbital fringe
process
process
.
The orbital fringe created according the

9. •
Phase unwrapping
.
. The phase distributed 0 to 360 ,Therefore, the phase
must be integrated. However, it is difficult to process
by influence of the noise. Some method were
proposed, but the best one is unknown
.
Conversion phase to DTM
Convert from the integrated phase to elevation value
according to the below equation
:
.
process

10. Fundamental of DTM Generation
by Interferometry SAR

11. equations of DTM Generation
equations of DTM Generation
The difference of the slant length of SAR 1 and SAR 2 is
The difference of the slant length of SAR 1 and SAR 2 is
approximated the next equation
approximated the next equation
the relation of difference of phase and elevation value
shows the nest equation
Then, the elevation values are calculated by the following equation
according to the geometry of interferometry

12. Fundamental equations of DTM Generation
Fundamental equations of DTM Generation
by Interferometry SAR
by Interferometry SAR
•
The equation 4 shows the proportion of different
The equation 4 shows the proportion of different
phase against the change of the slant range
phase against the change of the slant range
The equation 5 shows the relation of phase difference and
elevation

13. DTMs: accuracy
DTMs: accuracy
Model built
Model built
using the whole
using the whole
data set:
data set:
reference model
reference model
Model built
Model built
using a subset of
using a subset of
the data:
the data:
approximated
approximated
model
model

14. DTMs: approximation error
DTMs: approximation error
Maximum diference
Maximum diference
Calculate all differences between
Calculate all differences between
elevation data and interpolated
elevation data and interpolated
data
data

15. Error assessment for Digital
Terrain Models
(non-interferometey)
1
1.Errors produced when heights are
.Errors produced when heights are
interpolated from digitiszd contours
interpolated from digitiszd contours
.
.
2
2.Differences in the results produce by
.Differences in the results produce by
different algorithms for estimating terrain
different algorithms for estimating terrain
characteristics such as gradient or aspect
characteristics such as gradient or aspect

16. InSAR DTM ACCURACY
InSAR DTM ACCURACY
•
The accuracy of an interferometrically
The accuracy of an interferometrically
generated DTM is determined by these
generated DTM is determined by these
three factors
three factors
:
:
1
-
Measurement accuracy of the phase
of a pixel
2
-
Accuracy of the imaging geometry
3
-
constancy of the wave propagation
conditions

17. Phase Accuracy
Phase Accuracy
Phase noise originates from different sources, the dominant ones
being
:
1
-
System noise, e.g. thermal receiver noise and
quantization noise: These are the dominant noise
sources in single-pass interferometry
.
2
-
Temporal scene decorrelation: In repeat-pass
interferometry the sub-resolution properties of the
imaged scatterer may change between surveys,
e.g. by movement of leaves and branches, water

18. Orbit accuracy
Orbit accuracy
•
Insufficient accuracy in the sensor position gives rise to
Insufficient accuracy in the sensor position gives rise to
smooth large-scale terrain reconstruction errors
smooth large-scale terrain reconstruction errors
a horizontal or vertical shift of the entire interferometer
by a certain amount will result in the same shift of the
reconstructed terrain
.
An orbit error component that effectively rotates the interferometer
baseline will also rotate the DTM
.

19. Propagation Effects
Propagation Effects
•
Repeat-pass interferometry relies on the constancy of the wave
Repeat-pass interferometry relies on the constancy of the wave
propagation conditions for the two acquisitions
propagation conditions for the two acquisitions
1
_
Tropo5pheric water vapour may cause phase shifts in interferograms.
In a high percentage of data sets cloud-like or ripple-like phase
structures can be found. The amount of phase error is most often
much smaller than 0.5 fringe cycles. Often, this kind of error can be
averaged out, since several interferograms of the same area are
usually required for DTM generation, anyway
.
2
_
In a small fraction of SAR data localised phase errors due to
convective cells of water vapour have been observed. Their extent are
less than 30 km; the phase error can be 1 ... 3 fringes. Their special
structure allows to identify them easily and discard these areas from
the interferogram
.
3
_
The influence of the iono5phere is not yet well understood.
Ionospheric waves are often triggered in arctic regions and propagate
to lower latitudes

20. Reconstructed Ft.Irwin DTM
Reconstructed Ft.Irwin DTM

21. Magnitude ERS SAR image of Mojave Desert
Magnitude ERS SAR image of Mojave Desert
CA, USA. Size==40km x 40km
CA, USA. Size==40km x 40km

22. Contour
Contour line
line & fringe
& fringe
Fringe Contour line
of generated
DTM

23. •
The SAR imaging process maps the 3-D object, e.g. the
The SAR imaging process maps the 3-D object, e.g. the
Earth's surface, into the 2-D radar co-ordinates
Earth's surface, into the 2-D radar co-ordinates range
range and
and
azimuth.
azimuth. Rang
Rang

24. Azimuth & Range
Azimuth & Range

25. DTM profile
DTM profile
•
Real line: topographic line
Real line: topographic line
•
DTM Break line: generated
DTM Break line: generated
Azimuth
direction
Range
direction

27. Tkanks
Thanks