Using parallax in remote sensing to determine cloud feature height
View Patent ↗Techniques for using small parallax angles in remote sensing to determine cloud feature height include exploiting two identical medium-resolution SWIR bands with parallax to estimate cloud edge feature heights well enough to enable assessments of the impacts of shadows and proximate cloud scattering on ground illumination, and hence, on reflectance calculations. The bands are intentionally designed to have a suitable parallax angle, in one embodiment approximately 1.5 degrees. With this parallax, one band will see more ground pixels than the other band as they encounter a leading edge of a cloud and the other band will see more ground pixels than the one band as they encounter the lagging edge of the cloud. From these numbers of pixels, the height of the leading and lagging edges of the cloud can be determined.
1. A method of determining the height above ground of an object in the sky, comprising:
collecting from a position above the surface of the Earth light energy coming from a first direction;
collecting from a position above the surface of the Earth light energy coming from a second direction, wherein the second direction is not parallel to the first direction;
comparing the light energy from the first direction and the second direction to determine when an object in the sky is encountered, and determining a measure of the difference between the light energy from the two directions when the object is encountered; and
calculating the height above Earth of the object based on the measure of the difference;
wherein each of the collecting operations is performed by at least one row of multiple, separate pixels, there being at least one row for the collecting in the first direction and at least one row for the collecting in the second direction.
2. A method as defined in claim 1 , wherein the light energy collected from the two directions is of approximately the same wavelength.
3. A method as defined in claim 1 , wherein the light energy is in the SWIR range of the electromagnetic spectrum.
4. A method as defined in claim 1 , wherein the angle between the first and second directions is less than 5 degrees.
5. A method as defined in claim 1 , wherein the angle between the first and second directions is within a range between 1.0 and 2.0 degrees.
6. A method as defined in claim 1 , wherein the light energy is ambient light.
7. A method of determining the height above ground of an object in the sky, comprising:
collecting from a position above the surface of the Earth light energy coming from a first direction;
collecting from a position above the surface of the Earth light energy coming from a second direction, wherein the second direction is not parallel to the first direction;
comparing the light energy from the first direction and the second direction to determine when an object in the sky is encountered, and determining a measure of the difference between the light energy from the two directions when the object is encountered; and
calculating the height above Earth of the object based on the measure of the difference;
wherein the comparing operation includes:
comparing the light energy from the first direction and the second direction to determine when a leading edge of an object in the sky is encountered, and determining a measure of the difference between the light energy from the two directions when the leading edge is encountered;
comparing the light energy from the first direction and the second direction to determine when a lagging edge of an object in the sky is encountered, and determining a measure of the difference between the light energy from the two directions when the lagging edge is encountered;
and wherein the calculating operation includes:
calculating the height of the leading edge of the object based on the measure of the difference between the light energy from the two directions when the leading edge is encountered; and
calculating the height of the lagging edge of the object based on the measure of the difference between the light energy from the two directions when the lagging edge is encountered.
8. A method as defined in claim 7 , further including:
interpolating the height between the calculated height of the leading edge and the calculated height of the lagging edge.
9. A method as defined in claim 7 , wherein the angle between the first and second directions is within a range between 1.0 and 2.0 degrees.
10. A method as defined in claim 7 , wherein the light energy is ambient light.
11. A method as defined in claim 7 , wherein the light energy collected from the two directions is of approximately the same wavelength.
12. A method as defined in claim 7 , wherein the light energy is in the SWIR range of the electromagnetic spectrum.
13. A method as defined in claim 7 , wherein the angle between the first and second directions is less than 5 degrees.
14. A method of determining the height above ground of an object in the sky, comprising:
collecting from a position above the surface of the Earth light energy coming from a first direction;
collecting from a position above the surface of the Earth light energy coming from a second direction, wherein the second direction is not parallel to the first direction;
comparing the light energy from the first direction and the second direction to determine when an object in the sky is encountered, and determining a measure of the difference between the light energy from the two directions when the object is encountered; and
calculating the height above Earth of the object based on the measure of the difference;
wherein the determining operation of the comparing operation includes determining the number of pixels on the ground that can be seen in one of the first and second directions that cannot be seen on the ground in the other of the directions.
15. A method as defined in claim 14 , wherein the pixel determination includes determining to an amount less than one pixel.
16. A method as defined in claim 14 , wherein the light energy collected from the two directions is of approximately the same wavelength.
17. A method as defined in claim 14 , wherein the light energy is in the SWIR range of the electromagnetic spectrum.
18. A method as defined in claim 14 , wherein the angle between the first and second directions is less than 5 degrees.
19. A method as defined in claim 14 , wherein the angle between the first and second directions is within a range between 1.0 and 2.0 degrees.
20. A method as defined in claim 14 , wherein the light energy is ambient light.
21. A method of determining the height of a cloud, comprising:
providing a pair of radiant energy sensors at a height greater than the cloud, the sensors being directed toward the cloud at a small parallax angle relative to each other, the parallax angle being less than 5 degrees;
receiving radiant energy with the sensors; and
comparing the radiant energy received by the two sensors to determine the height of the cloud.
22. A method as defined in claim 21 , wherein the pair of sensors are in a single satellite.
23. A method as defined in claim 22 , wherein the satellite is flying in a low Earth orbit.
24. A method as defined in claim 21 , wherein the pair of sensors is in a single aircraft.
25. A method as defined in claim 24 , wherein the aircraft is an unmanned vehicle.
26. A method as defined in claim 21 , wherein the radiant energy is ambient radiant energy.
27. A method of determining the height above ground of an opaque cloud in the sky, comprising:
providing a multi-band line scanning imager with first and second SWIR sensor bands that are aligned in such a way that the two bands are parallel in the cross-scan direction, but non-parallel with a small, but non-zero, parallax angle in the in-scan direction;
collecting radiant energy with the imager from a moving above-ground platform that is further from the ground than an opaque cloud;
forming separate ortho-rectified, co-registered SWIR images, based on collected sensor data from the first and second bands;
forming separate ortho-rectified, co-registered classification images, based on the first and second SWIR images, that classify each pixel within each image as either opaque cloud, snow/ice, or other;
comparing the first and second classification images to identify in-scan segments of pixels where corresponding pixels in both of the first and second classification images has been classified as opaque cloud, leading to further classification of these pixels as opaque cloud interior pixels;
comparing the first and second classification images to identify in-scan segments of pixels where corresponding pixels in one of the first and second said classification images has been classified as opaque cloud and the corresponding pixels in the other of the first and second classification images has been classified as snow/ice or other, leading to further classification of these pixels as opaque cloud edge pixels; and
based on the opaque cloud edge pixels and the opaque cloud interior pixels, determining the height above ground of the opaque cloud edge pixels.