Method for determining the water content in the atmosphere, method for detecting icing conditions and computer programs

1. A method for determining the water content in the atmosphere by processing images acquired by an out-of-focus interferometric imaging device, said device being solely able to image water and ice particles having a size lying in a given range of sizes, said method comprising the following steps:

a) obtaining at least one of the images produced by the out-of-focus interferometric imaging device;

b) determining the number of particles lying in the given range of sizes from said at least one of the images;

c) measuring the mass of particles having a size lying in the given range of sizes from the number of particles determined;

d) estimating the mass of particles having a size outside the given range of sizes, said estimation step comprising the following steps:

i) determining the number of particles having a size equal to a threshold size;

ii) evaluating the number of particles outside the given range of sizes from the number of particles determined during step i) and from the threshold size; and

iii) estimating the mass of the particles outside the given range of sizes from the number of particles evaluated; and

e) determining the water content in the atmosphere by adding the estimated mass and the measured mass.

2. The method for determining the water content in the atmosphere according to claim 1 , in which the number of particles evaluated during step ii) is considered to be constant and equal to the number of particles determined at step i) having a size equal to the threshold size.

3. The method for determining the water content in the atmosphere according to claim 1 , in which said method is implemented by a processing unit comprising a calculation unit and a storage unit, said storage unit comprising at least a predetermined distribution of the number of particles according to the size of these particles outside said given range of sizes, said predetermined distribution comprising a number of particles having said threshold size, and in which the number of particles is evaluated by multiplying the predetermined distribution by the ratio between the number of particles determined at step i) and the number of particles in said distribution having said threshold size.

4. A computer program containing instructions for implementing the determination method according to claim 1 , when it is executed by a processor.

5. The method for determining the water content in the atmosphere according to claim 1 , in which the number of particles is evaluated during the step ii) by polynomial extrapolation from a plurality of numbers of particles determined at step i) and from the size of these particles.

6. The method for determining the water content in the atmosphere according to claim 5 , in which the polynomial extrapolation uses a logarithmic equation.

7. The method for determining the water content in the atmosphere according to claim 1 , in which the given range of sizes is between 50 micrometres and 1000 micrometres.

8. The method for determining the water content in the atmosphere according to claim 7 in which the given range of sizes is between 70 micrometres and 700 micrometres.

9. The method according to claim 1 which further detects icy atmospheric conditions, the method further comprising the following steps:

receiving an external temperature value; and

detecting icy atmospheric conditions from the water content and the external temperature value.

10. A computer program containing instructions for implementing the detection method according to claim 9 , when it is executed by a processor.

11. The method for determining the water content in the atmosphere according to claim 1 , in which the number of particles is evaluated during step ii) by linear extrapolation from a predefined size beyond which there are no longer any particles in the atmosphere.

12. The method for determining the water content in the atmosphere according to claim 11 , in which the particles are water particles, and the predefined size is substantially equal to 2300 micrometres.

13. The method for determining the water content in the atmosphere according to claim 12 , in which, when the particles are ice particles, the predefined size is substantially equal to 2700 micrometres.

14. The method for determining the water content in the atmosphere according to claim 11 , in which, when the particles are ice particles, the predefined size is substantially equal to 2700 micrometres.