Estimating biofilm biomass on objects in an aquatic environment
System and method for estimating aquatic environment-originating biofilm biomass on a coating of an object. The method includes obtaining one or more digital images of a fouled portion of the coating on the object and determining from each of the one or more images a respective reflectance value for the portion of the coating. The method includes determining on the basis of the one or more reflectance values a value of a spectral index representative of biomass and calculating a biomass pigment surface area density on the basis of the spectral index, SI, and one or more calibration values determined for a reference coating. The method includes compensating the calculated biomass pigment surface area density for the reflectance of the coating of the object by applying a compensation associated with the difference of the reflectance of the coating of the object relative to the reference coating.
1 . A method for estimating aquatic environment-originating biofilm biomass on a coating of an object, including:
a) obtaining one or more digital images of a fouled portion of the coating on the object using a digital camera or imager,
b) determining from each of the one or more images a respective reflectance value for the portion of the coating;
c) determining on the basis of the one or more reflectance values a value of a spectral index representative of biomass;
d) calculating a biomass pigment surface area density on the basis of the spectral index, SI, and one or more calibration values determined for a reference coating; and
e) compensating the calculated biomass pigment surface area density for the reflectance of the coating of the object by applying a compensation associated with the difference of the reflectance of the coating of the object relative to the reference coating thereby generating a compensated biomass pigment surface area density;
f) producing a map of biofilm biomass on the fouled portion of the coating of the object from the compensated biomass pigment surface area density.
2 . The method of claim 1 , wherein the compensation is based on a comparison reflectance value representative for the coating underlying the biofilm biomass.
3 . The method of claim 2 , wherein the comparison reflectance value is:
a reflectance value determined for a part of the coating of the object from which all biomass had been removed;
a reflectance value determined from a reference object; or
a reflectance value stored in a database.
4 . The method of claim 1 , wherein each of the one or more images is obtained in a spectral band.
5 . The method of claim 4 , wherein the compensation is based on a comparison reflectance value representative for the coating underlying the biofilm biomass, the comparison reflectance value being a minimum value of the reflectance value for the coating underlying the biofilm biomass in the one or more spectral bands.
6 . The method of claim 4 , wherein at least one of the spectral bands is chosen to encompass an absorption wavelength of chlorophyll, or at least one of the spectral bands is chosen to exclude an absorption wavelength of chlorophyll.
7 . The method of claim 4 , wherein at least one of the spectral bands is chosen around 433, 460, 496, 555, 584, 601, 673, or 800 nm.
8 . The method of claim 1 , wherein in step e) the estimated biomass pigment surface area density on the coating, biomass current , can be determined from the biomass calculated from the Spectral Index, biomass SI , determined in step d) by an Error Factor, EF current , and Baseline Error BE current , from the equation
biomass
curr
e
n
t
=
biomass
SI
*
(
1
-
(
E
F
current
1
+
E
F
current
)
)
-
B
E
c
u
r
r
e
n
t
.
9 . The method of claim 8 , wherein the spectral index, SI, is one of:
coating normalized red reflectance defined as
SI
=
rNorm
673
=
R
673
R
673
clean
;
Normalized Difference Vegetation Index defined as
SI
=
NDVI
=
R
800
+
R
673
R
800
-
R
673
;
wherein R673 is the determined reflectance value in the range of 605-740 nm; R800 is the determined reflectance value in the range of 720-900 nm; R673 clean is the reflectance value in the range of 605-740 nm at the coating of the object without biomass.
10 . The method of claim 9 , wherein
if the spectral index is the coating normalized red reflectance, EF current =0.26 ln(R current673 )−1.00; BE current =0.0862 ln(R current673 )+0.0164; and
if the spectral index is the Normalized Difference Vegetation Index, EF current =0.24 ln(R current673 )−0.83; BE current =0.025 ln(R current673 )+0.1025;
wherein R current673 is the reflectance value of the current coating at 673 nm.
11 . The method of claim 1 , wherein the spectral index includes a ratio of two reflectance values.
12 . The method of claim 1 , wherein the spectral index, SI, is one of:
coating normalized red reflectance defined as
SI
=
rNorm
673
=
R
6
7
3
R
6
7
3
c
l
e
a
n
;
Normalized Difference Vegetation Index defined as
SI
=
NDVI
=
R
8
0
0
+
R
6
7
3
R
8
0
0
-
R
6
7
3
;
wherein R673 is the determined reflectance value in the range of 605-740 nm; R800 is the determined reflectance value in the range of 720-900 nm; R673 clean is the reflectance value in the range of 605-740 nm at the coating of the object without biomass.
13 . The method of claim 12 , wherein in step d) the pigment surface area density is determined from
pigment
surface
area
density
=
(
SI
-
c
a
)
1
b
,
wherein a, b and c are calibration values.
14 . The method of claim 13 , wherein
if the spectral index is the coating normalized red reflectance,
a=−1.921, b=0.093, c=2.477; and
if the spectral index is the Normalized Difference Vegetation Index,
a=0.618, b=0.240, c=−0.321.
15 . The method of claim 1 , wherein in step d) the pigment surface area density is determined from
pigment
surface
area
density
=
(
SI
-
c
a
)
1
b
,
wherein a, b and c are calibration values.
16 . The method of claim 1 , wherein the one or more digital images are obtained using a submarine.
17 . The method of claim 1 , wherein the camera is a hyperspectral camera and the one or more digital images are hyperspectral images.
18 . A system for estimating aquatic environment-originating biofilm biomass on a coating of an object, including a digital camera or imager and a processor configured for:
obtaining one or more digital images of a fouled portion of the coating on the object;
determining from each of the one or more images a respective reflectance value for the portion of the coating;
determining on the basis of the one or more reflectance values a value of a spectral index representative of biomass;
calculating a biomass pigment surface area density on the basis of the spectral index, SI, and one or more calibration values determined for a reference coating; and
compensating the calculated biomass pigment surface area density for the reflectance of the coating of the object by applying a compensation associated with the difference of the reflectance of the coating of the object relative to the reference coating thereby generating a compensated biomass pigment surface area density;
wherein a map of biofilm biomass on the fouled portion of the coating of the object is produced from the compensated biomass pigment surface area density.
19 . The system of claim 18 , wherein the camera is a hyperspectral camera and the one or more digital images are hyperspectral digital images.