ctra of these coral targets 
n. All corals have central 
ainent peak at 1070 nm. 
ristic absorption features 
n) and at 975 nm (water 
at 675 nm is followed by 
on. As per the spectral 
eight coral targets can be 
p A consisting of Favia, 
oup B comprising of 
(Live) and Group C: the 
massive and encrusting 
osure of soft, live coral 
lites. Two of the Group B 
senting massive and sub- 
xposure of the soft, live 
ite corallites. Turbinaria 
ose colony with more of a 
ral polyps. Group C: the 
me with polyps largely 
Plot: Key 
Favia 
Symphyllia 
Goniopora 
Porites 
Goniastrea 
Platygyra 
Turbinaria 
Turbinaria (bleached) 
a. 
2 
3 
- 4. 
5 
6 
7 
- 8 
    
50 1050 1150 1250 1360 
  
  
the sampled coral targets 
orm of in situ live coral 
of 1.7 cm. The individual 
tely parallel to each other 
terms of their spectral 
least reflectance over the 
ed by Goniastrea, Porites 
hest reflectance. In visible 
e “brown mode” of coral 
terized by “triple-peaked 
Ayers et al. in 1999. This 
ally exhibit a depressed 
and triple peaks or local 
50 nm. Group A corals 
absorption feature at 675 
izing endo-symbiont algae 
sues (Holden and LeDrew, 
) nm) these corals show à 
urve with central maxim? 
pt, steep rise between 6) 
ncreases to 820 nm with 
  
  
    
   
    
    
    
    
    
     
    
    
    
    
  
      
     
    
  
    
    
   
  
  
   
   
  
   
   
    
      
    
     
  
   
   
   
   
     
characteristic spike located near 760 to 762 nm. This spike is 
however a contribution from the atmospheric oxygen and brings 
out the limitation of the instrument to outweigh this spike while 
sensing and recording the target spectra. Favia spectra shows a 
small hump at 728 nm which is absent in rest of the Group A 
corals. The spectra show a rapid descent from 820 to 840 nm 
followed by a gradual descent over 840 to 910 nm region. Beyond 
910 nm the spectra are characterized by a steep descent to the 
water absorption feature located at 975nm. The absorption band 
depth appears to be a function of the depth of overlying water 
column. In the MIR region, the spectra show similar symmetrical 
pell-shape architecture with central maxima located at 1070 nm. 
Beyond 1150 nm upto 1350 nm the spectra show a featureless 
straight line trend except Platygyra which show a plateau at 1270 
nm. 
In case of Group B corals, the spectral architecture as shown by 
the Group A corals get considerably modified in the NIR region. 
The triple-peaked pattern is quite pronounced in case of 
Turbinaria and Goniopora while gets subdued for Symphillia. In 
NIR region these corals exhibit a hump at 725 nm which from 
Group À only Favia showed at 728 nm. Contrary to the Group A 
corals’ steady rise from 710 nm to 820 nm Group B corals show a 
peak and valley pattern in this region. Group B corals exhibit a 
pronounced descent from 820 to 840 nm deviating from the 
Group A trend of gradual descent over 840 to 910 nm. Turbinaria 
and Goniopora show a steep, stepped fall from 840 to 890 nm, 
900 to 930 nm and 933 to 999 nm interrupted by small spikes at 
898 nm and 933nm. This is due to the ripple effect of the water 
column present on the targets. The water absorption trough 
centered at 975 nm is present for both. Symphyllia though 
conforms to the trend of steady descent from 820 to 840 nm but 
deviates from the Group B trend in 840 to 950 nm region by 
showing a convex drop upto 935 nm. The water absorption 
feature of Symphyllia is absent from display in the 950 to 1000 
nm region because of negative reflectance values indicating a 
strong water column absorption since this coral was submerged 
under 8 cm water column- the maximum recorded on field. In 
MIR region, however, Group B corals conform to the trend of 
Group A corals. 
Grup C represented by the bleached coral spectrum of 
Turbinaria is characteristically different from the live corals in 
UV-Visible region with relatively much higher reflectance values, 
shooting up to its maximum at 590 nm (six times as that of its live 
counterpart). Right from 350 to 600 nm the bleached coral 
Spectrum rises steadily with minor breaks of slopes. Between 590 
and 650 nm, this spectrum again show a stepped pattern of 
descent with intermittent breaks of slopes. Thereafter, it plunges 
down to the chlorophyll absorption trough located at 675 nm. 
Unlike the live coral spectra, the bleached coral spectrum has a 
Stepped rise up to 710 nm. Beyond 715 nm to 1350 nm this 
Spectrum closely follows the trend of live Turbinaria with 
characteristic local shoulders and troughs getting vertically 
pronounced, 
In order to exaggerate the spectral shapes and enhance the subtle 
features of the zero-order spectra, the first and second order 
derivatives (Figure 6 and 7 respectively) were numerically 
calculated over 4nm as finite band resolution. Figure 6 shows 700 
and 760 nm as the locations corresponding to peaked coral 
reflectance for all the eight corals. However, the peak at 760 nm 
   
is not a contribution from the target. In the visible region two 
peaks out of that triple peak at 575 and 600 nm also become 
prominent in the first derivative spectra. The first order 
derivatives also bring out the characteristic absorption troughs 
located over 650 to 675 nm, 800 to 850 nm, 900 to 950 nm and 
1100 to 1150 nm for all the eight corals. Moreover, the first 
derivative of averaged reflectance appears to provide a good 
separability between bleached and live corals over a large spectral 
region from 430 to 590 nm. At 631 and 647 nm the first 
derivative values of all the live corals are negative while for the 
bleached coral it is positive. 
  
2.08.7 Plot: Key 
Favia 
0.05 — 
M 
Symphyllia 
Goniopora 
Porites 
e 
GOL e ia ui m n bo Ln cd 
0.03 — — Goniastrea 
= Platygyra 
Turbinaria 
Turbinaria (bleached) 
0.02 4 
DOGS 
0.01 7 
0 d en ei I: 
  
First Derivative 
-0.01 4 
  
-0.02 4 
-0.03 4 
  
-0.04. 4 
  
-0.05 
  
I T T T T T I E I ] 
350 | 450 550 650 750 850 950 1050 1150 1250 1350 
  
  
Wavelength (nm) 
  
Figure 6. First derivatives of the sampled coral spectra 
The second derivative of the averaged reflectance identifies 680 
to 700 nm region as a window to separate live and bleached coral 
spectra. In this region all the live corals record a positive second 
derivative value while the bleached coral has a negative value. 
The second derivative plot also shows the enhanced reflectance 
and absorption features of Symphyllia which rather showed a 
subdued zero-order signal because of the maximum water 
column. 
  
0.020 
0.015 
0.010 
0.005 
0.000 ].7—— ro ee on Phat. 
  
-0.005 
Plot: Key 
1. Favia 
2. Symphyllia 
3. Goniopora 
4. Porites 
—— 8. Goniastrea 
e 
7 
8 
Second Derivative 
-0.010 
-0.015 
Platyayra 
Turbinaria 
Turbinaria (bleached) 
-0.020 
  
-0.025 
  
30.030 T T T T- T T T 1 
350 450 550 850 750 850 950 1050 1150 1250 1350 
  
Wavelength (nm) 
  
  
  
Figure 7. Second derivatives of the sampled coral spectra 
5. CONCLUSIONS 
The results obtained in this preliminary study suggests that in situ 
hyperspectral signatures of corals can be used as an essential 
input to study the spectral behaviour of reef building corals. All 
seven live corals conform to the general belief of strong reflection