Truck Characteristics Analysis from All Aspect Angles with Quad-pol Radarsat-2 Images

ZHANG Bo, WANG Chao, ZHANG HongJuly 26, IGRASS 2011

Outline

• Motivation• Experiment data• Analysis method and discussion• Conclusion

Outline

• Motivation• Experiment data• Analysis method and discussion• Conclusion

Motivation

Motivation

[1] Gintautas Palubinskas and Hartmut Runge. Rasar Signatures of a Passenger CAR. IEEE Geoscience and Remote Sensing Letters, Vol.4,No.4,2007[2] D. Hounam, S. Baumgartner, K. H. Bethke, M. etc. , “An autonomous, non-cooperative, wide-area traffic monitoring system using space-based radar (TRAMRAD),” in Proc. IGARSS, Seoul, Korea, Jul. 2005, pp. 2917–2920.

Motivation

Their researches are based on the air-born E-SAR data.

Outline

• Motivation• Experiment data• Analysis method and discussion• Conclusion

Experiment data

Site Center frequency

(Hz)

Pixel space (m) (RA)

Incidence angle

Orbit Range bandwidth

(Hz)

Look numbe

rs

Hainan 5.4E9 4.734.9222.16°-24.09

°Ascending 3.0E7 11

Jiangsu 5.4E9 4.734.7438.37°-39.84

°Descending 3.0E7 11

Hubei 5.4E9 4.735.0647.56°-48.74

°Descending 3.0E7 11

（ A）Medium truck （ B） Carriage （ C） larger truck （ D） Tank truck

Radarsat-2 quad polarimetric SAR images

what size of the truck can be detected?

How to change the characteristics with aspect angle? How do truck structure

affect characteristics?

Experiment data

23.2°

39.7°

48.1°

23.2°

Truck size

8.7， 2.3， 3.4

5.7, 2.2, 2.6

11.9, 2.5, 3.8

15.8, 2.5, 3.98

10.9, 2.47, 3.22

Aspect angleIncidence angle Background

soil-rock mixture roadbed

Asphalt road

Concrete road

Time

2009-2

2009-4

2009-9

2010-3

2010-6

2010-10

Outline

• Motivation• Experiment data• Analysis method and discussion• Conclusion

Analysis methods and discussion

Z

SAR Orbitx

y

True north

Magnetic north

Truck heading

θ

SAR swath width

Incidence angle

A

ΔA

ΔB

aspect angle: ∠S = A + ∆A+∆B

A : measured by compass

∆A: local magnetic declination

∆B:

inverse calculated by the four corners’ geographic coordinates in SAR image

Incidence angle: Calculated on the ellipsoid surface

Analysis methods and discussionAspect angle Intersection angle

As the left and right sides of truck are symmetrical, the scope of aspect angle can be reduced from [0, 360] to [0, 180].

The front and rear shape of truck are almost similar. To facilitate comparison, the aspect angle can be approximately replaced by the minimum intersection angle which is the angle between x-direction and long side of truck. So the intersection angle is in the range of [0, 90].

0/0,225/45,270/90

180/0,225/45,270/90

181/1,193/13,206/26217/37,223/43,229/49239/59,251/71,262/82,272/92

2/2,351/9,151/29,45/45

Analysis methods and discussion

2 2 2 2

hh hv vh vvSPAN = S + S + S + S

[ , , , ]

1( ( ))

2hh vv hh vv hv vh vh hvvh

k a b c d

S S S S S S i S S

=

= + − + −

0 0,

( , ) ( , )c t

x y dxdy x y c tσ σ σ+∞ +∞

−∞ −∞

= ≈ ∆ ⋅∆ ⋅∑∫ ∫yx ∆⋅∆

the area of one pixel in SAR image

( )0,,

c tc tσ∑ stands for the area integral at the position of (c, t)

Discussion of SPAN value

A

B

C

D

Four types truck SPAN value characteristic pattern with intersection angle and incidence angle.

Incidence angle: A < C < D

Truck size : A < C < D

SPAN value: D < A < C

which factor is more impacted on RCS value within incidence angle and size?

structure is the key factor

Discussion of background value

Four types truck SPAN value characteristic

For the wavelength of Raradarsat-2 beam is 5.5 cm and roads are relatively smooth, the clutter of background shows lower at larger incidence angle, which will improve truck detection ratio. Considering the impact of incidence angle on the translation of slant range to ground range, it can be concluded that same truck will occupy more pixels on slant range and bring stronger backscatter on larger incidence angle image. In short, the larger incidence angle SAR image will be more favorable to truck detection.

Discussion of the impact aspect angle

the higher SPAN value between 43° and 71° is due to the odd bounce which may be caused by the rough truck tarpaulin roof.

the even bounce is always bigger than other Pauli components except at the intersection angle around 45°.

The smooth and bare cylindrical structure of tank truck lead to the odd backscatter bounce very weak.

Conclusion

Structure rather than size is the key factor which affects the truck characteristics.

When the truck heading turning form perpendicular to parallel to the SAR illumination, the even bounce intensity will be decreased at first and then increased, the alter angle is 45°.

Incidence angle also impact the RCS value. But its impact on the background will be even greater . it can be confident that SAR image at larger incidence angle is beneficial to increase the detection ratio for truck detection.

RCSRCS

Structure

Incidence angle

Aspect angle