16 Reefscape Ecology Within the South Pacific
251
Table 16.1 Spectral
specificities of the sensors
QuickBird-2 (QB-2) and
WorldView-2 (WV2)
Band name
Wavlengths QB-2 (nm) Wavelengths WV-2 (nm)
Purple
400–450
Blue
450–520
450–510
Green
520–600
510–580
Yellow
585–625
Red
630–690
630–690
NIR 1
705–745
NIR 2
760–890
770–895
NIR 3
860–1,040
Panchromatic 450–900
450–800
16.2.3.2 Ground-Truthing
Whilst the coral cover was measured based on the methods of permanent photoquadrat and manta tow, the landscape structure was identified through the panoramic
survey method.
In order to connect the products of remote sensing and bathymetry, the depth measurements were acquired to calibrate and validate the digital depth model (DDM). A
0.1 m accuracy acoustic system (sonar Lowrance LMS-527 CDF iGPS) was mounted
on a 5 m length aluminum boat. Each acoustic measurement was collected at mild
conditions regarding the swell and wind, to optimize the vertical acquisition. The
datum used was the WGS-84 and projection was referenced according to the UTM
Zone 6 South.
16.2.3.3 Remotely-Sensed Imagery
Two datasets were used for the purpose of the study, a QuickBird-2 (QB-2) dataset,
acquired 9 November 2006, and a WorldView-2 (WV-2) dataset, acquired 17 March
2010. Whilst the QB-2 dataset includes four bands (three in the visible and one in
the infrared spectrum) processed at 0.6 m, the WV-2 dataset leverages eight bands
(five visible and three infrared) processed at 0.5 m (Table 16.1).
The processing carried out to achieve this very high spatial resolution (VHR)
stemmed from the enhancement method called pansharpening. Based on the purple
band, showing the highest entropy index and the lowest attenuation by water, the
Gram-Schmidt algorithm enabled the QB-2 and WV-2 multispectral bands of 2.4
and 2 m resolution, respectively, to be merged with the panchromatic band of 0.6
and 0.5 m resolution, respectively (see Collin and Planes 2012). Given the obvious
roughness of the water surface driven by wind, a sun glint procedure has been applied
to the QB-2 dataset (Fig. 16.5). Based on the assumption that only the specular
reflection induced by waves is recorded by the infrared channel, it is possible to
correct each of the three visible bands (Hedley et al. 2005). This leads to the following
equation:
L i (V ) corr = L i (V ) − a i × [L(NI R) − L min (NI R)]
(16.1)
251
Table 16.1 Spectral
specificities of the sensors
QuickBird-2 (QB-2) and
WorldView-2 (WV2)
Band name
Wavlengths QB-2 (nm) Wavelengths WV-2 (nm)
Purple
400–450
Blue
450–520
450–510
Green
520–600
510–580
Yellow
585–625
Red
630–690
630–690
NIR 1
705–745
NIR 2
760–890
770–895
NIR 3
860–1,040
Panchromatic 450–900
450–800
16.2.3.2 Ground-Truthing
Whilst the coral cover was measured based on the methods of permanent photoquadrat and manta tow, the landscape structure was identified through the panoramic
survey method.
In order to connect the products of remote sensing and bathymetry, the depth measurements were acquired to calibrate and validate the digital depth model (DDM). A
0.1 m accuracy acoustic system (sonar Lowrance LMS-527 CDF iGPS) was mounted
on a 5 m length aluminum boat. Each acoustic measurement was collected at mild
conditions regarding the swell and wind, to optimize the vertical acquisition. The
datum used was the WGS-84 and projection was referenced according to the UTM
Zone 6 South.
16.2.3.3 Remotely-Sensed Imagery
Two datasets were used for the purpose of the study, a QuickBird-2 (QB-2) dataset,
acquired 9 November 2006, and a WorldView-2 (WV-2) dataset, acquired 17 March
2010. Whilst the QB-2 dataset includes four bands (three in the visible and one in
the infrared spectrum) processed at 0.6 m, the WV-2 dataset leverages eight bands
(five visible and three infrared) processed at 0.5 m (Table 16.1).
The processing carried out to achieve this very high spatial resolution (VHR)
stemmed from the enhancement method called pansharpening. Based on the purple
band, showing the highest entropy index and the lowest attenuation by water, the
Gram-Schmidt algorithm enabled the QB-2 and WV-2 multispectral bands of 2.4
and 2 m resolution, respectively, to be merged with the panchromatic band of 0.6
and 0.5 m resolution, respectively (see Collin and Planes 2012). Given the obvious
roughness of the water surface driven by wind, a sun glint procedure has been applied
to the QB-2 dataset (Fig. 16.5). Based on the assumption that only the specular
reflection induced by waves is recorded by the infrared channel, it is possible to
correct each of the three visible bands (Hedley et al. 2005). This leads to the following
equation:
L i (V ) corr = L i (V ) − a i × [L(NI R) − L min (NI R)]
(16.1)