Method and system for remotely measuring the volume of liquid stored in external floating roof tanks
A method for measuring a liquid volume and/or corresponding fill rate of floating roof tanks includes selecting an Area Of Interest (AOI) to be monitored at the earth's surface, gathering geographical coordinates of tanks in the AOI, and downloading and pre-processing a time series of SAR reference images covering the AOI. The method includes projecting geographical coordinates of the tanks on the time series of the images to determine pixel coordinates of the tanks, and determining tank dimensions through processing of the images at the pixel coordinates. The method includes downloading and pre-processing at least one new SAR image over the AOI and registering it on top of the reference images, and, for each tank of the AOI, detecting in the new SAR image a bright spot corresponding to the roof of the tank and converting its pixel coordinates into liquid volume and/or fill rate information.
1. A method for measuring the liquid volume and/or corresponding fill rate of floating roof tanks comprising:
a step of selecting an Area Of Interest (AOI) that will be monitored at the surface of the earth,
a step of gathering the geographical coordinates of the floating roof tanks in the AOI,
downloading and pre-processing a time series of SAR reference images covering the AOI,
projecting the geographical coordinates of the floating roof tanks on said time series of Synthetic Aperture Radar (SAR) reference images to determine pixel coordinates of the floating roof tanks in said images,
determining the dimensions of said floating roof tanks through processing of the SAR reference images at said pixel coordinates,
downloading and pre-processing at least one new SAR image over the AOI and registering it on top of the SAR reference images, and
for each floating roof tank of the AOI, detecting in the new SAR image a bright spot corresponding to the floating roof of said tank and converting its pixel coordinates into a liquid volume and/or fill rate information.
2. The method according to claim 1 , wherein an iterative process is run to refine the geographical coordinates and dimensions of the floating roof tanks, when determining the pixel coordinates of the floating roof tanks in the SAR reference images.
3. The method according to claim 1 , wherein the detection of a bright spot in the new SAR image is performed by detecting said spot in an image window determined using the tank geographical coordinates and dimensions.
4. The method according to claim 1 , wherein the liquid volume and/or fill rate information is determined from the height of the floating roof, said height of the floating roof being computed as a function of the bright spot position.
5. The method according to claim 4 , wherein the height of the floating roof is computed as a function of the distance between the bright spot position and its position when the tank is empty.
6. The method according to claim 1 , wherein a de-bursting and/or a cropping of a SAR image is performed during a pre-processing step.
7. The method according to claim 1 , wherein the SAR images are satellite SAR images.
8. The method according to claim 1 , wherein optical images are processed to identify the floating roof tanks of the AOI and to determine their geographical coordinates.
9. The method according to claim 1 , wherein optical images are processed to determine the diameters of the floating roof tanks of the AOI, said diameters being refined by processing of the SAR reference images.
10. The method according to claim 1 , wherein optical images are initially processed to compute the boundaries of an Area Of Interest (AOI) as a polygon containing a set of neighboring tanks that can be seen on optical images.
11. The method according to claim 1 , wherein the geographical coordinates include latitude, longitude and altitude information and wherein the altitude information is extracted from a digital elevation model database.
12. The method according to claim 2 , wherein the coordinates refinement processing is performed through an iterative method maximizing the following energy:
E
(
λ
,
θ
,
z
,
r
,
h
)
=
∑
α
∈
[
0
,
2
π
]
u
(
P
(
λ
+
r
cos
α
,
θ
+
r
sin
α
,
z
)
+
u
(
P
(
λ
+
r
cos
α
,
θ
+
r
sin
α
,
z
+
h
)
)
where α spans over a regular sampling of [0, 2π]
with λ longitude of the tank center, θ latitude of the tank center,
z altitude of the center of the bottom of the tank, r radius of the tank,
and where u is the average image, obtained by averaging the SAR reference images pixel per pixel, and where P is the average projection function.
13. A system for measuring the volume and/or fill rate of floating-roof tanks comprising at least a computing tool to perform the following steps:
a step of selecting an Area Of Interest (AOI) that will be monitored at the surface of the earth,
a step of gathering the geographical coordinates of the floating roof tanks in the AOI,
downloading and pre-processing a time series of SAR reference images covering the AOI,
projecting the geographical coordinates of the floating roof tanks on said time series of SAR reference images to determine pixel coordinates of the floating roof tanks in said images,
determining the dimensions of said floating roof tanks through processing of the SAR reference images at said pixel coordinates,
downloading and pre-processing at least one new SAR image over the AOI and registering it on top of the SAR reference images, and
for each floating roof tank of the AOI, detecting in the new SAR image a bright spot corresponding to the floating roof of said tank and converting its pixel coordinates into a liquid volume and/or fill rate information.