CMRT09

Stilla, Uwe

Bibliographic data

Monograph

Persistent identifier:: 856955019

Author:: Stilla, Uwe

Title:: CMRT09

Sub title:: object extraction for 3D city models, road databases, and traffic monitoring ; concepts, algorithms and evaluation ; Paris, France, September 3 - 4, 2009 ; [joint conference of ISPRS working groups III/4 and III/5]

Scope:: X, 234 Seiten

Year of publication:: 2009

Place of publication:: Lemmer

Publisher of the original:: GITC

Identifier (digital):: 856955019

Illustration:: Illustrationen, Diagramme, Karten

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Monograph

Collection:: Earth sciences

Chapter

Title:: THEORETICAL ANALYSIS OF BUILDING HEIGHT ESTIMATION USING SPACEBORNE SAR-INTERFEROMETRY FOR RAPID MAPPING APPLICATIONS Stefan Hinz, Sarah Abelen

Document type:: Monograph

Structure type:: Chapter

In: Stilla U, Rottensteiner F, Paparoditis N (Eds) CMRT09. IAPRS, Vol. XXXVIII, Part 3/W4 — Paris, France, 3-4 September, 2009 Figure 7: pdf of height for varying coherence (other parameters fixed). 4. ACCURACY OF BUILDING HEIGHT ESTIMATION The accuracy assessment has been carried out with the scheme described above. Parameter values were chosen in accordance to the main TanDEM-X specifications. Mutual influence of following parameters has been investigated: baseline length incidence angle coherence amount of averaging/smoothing wavelength Figure 8 exemplifies the specific case of moderate coherence (0.6) and only one single look. i.e. the original spatial resolution is maintained and no smoothing is done. A low coherence has been chosen by intention, although significantly better values are expected for TanDEM-X, since clutter may decrease the coherence in layover areas. The ideal case for this configuration suggests to selecting a long baseline (e.g. 150m) and a steep incidence angle (15°), which results in a height accuracy of approx. 2.5m. Incidence angles less close to the system limits would yield an accuracy of 5m - 7m. The effect of improving coherence is illustrated in Figure 9, where height accuracy is plotted against coherence and various baselines. It can be seen that, for a baseline of 150m, height accuracy increases from 2.5m at a coherence of 0.6 up to 1.5m at a coherence of 0.9. The final assessment deals with the influence of the number of looks. A coherence of 0.7 for the case of 200m baseline and 15° incidence angle enables the derivation of building heights with lm accuracy for the given viewing geometry (see Figure 10). As this kind of averaging reduces the spatial resolution, it is reasonable to investigate the effect of smoothing onto the height accuracy only up to four looks. What is moreover evident from Figure 10 is that the increase of height accuracy is significant from one to two and three looks, but it is then gradually attenuating - especially for typical coherence values in the range of 0.6 - 0.8. As a last remark we refer to the used wavelength (X-band in our calculations). Equation 7 shows that the RADAR wavelength is a constant factor for the phase-to-height-sensitivity, which directly propagates to the standard deviation of height measurements. A longer wavelength (L-band for instance) yields a worse phase-to-height sensitivity and consequently a worse height accuracy. It should be noted, however, that long wavelengths generally yield better interferometric coherence depending on the scene characteristics. Hence, this effect could be partly compensated. Height Error for Correlation Coefficient = 0.6 and 1 Look Figure 8: Height accuracy for varying baseline and incidence angle while other parameters are fixed. Height Error for 1 Look and Incident Angle = 15® Figure 9: Height accuracy for varying baseline and coherence while other parameters are fixed. Figure 10: Height accuracy for varying looks and coherence while other parameters are fixed. 5. DISCUSSION AND CONCLUSION The above analysis shows that space-borne interferometric SAR systems like TanDEM-X will allow to measure vertical heights with a standard deviation of roughly 1,5m, which also holds for the case of moderate coherence in layover areas. Regarding the application of rapid mapping, this accuracy will certainly allow the estimation of the number of floors or the detection of changes in the 3D building geometry. However, baselines and incidence angles have to be chosen carefully, as they are close to the technical limits (i.e. “critical baseline” and steep viewing angle). These constraints can be relaxed when additional data in form of digital ground plans is available. These allow, for instance, the utilization of specialized filters instead of simple multi-looking. The geometry of the filter mask can then be adapted to the respective building shape to include as much pixels as possible as observations into the height measurement. Recall Figure 6 to see how the standard deviation of interferometric phase improves with increasing number of observations.

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