Distributed volumetric cargo sensor system

1. A method for detecting cargo within a cargo container that has a ceiling, a floor, and an interior space disposed between the ceiling and the floor, the method comprising:

(a) receiving a plurality of distance signals generated by a plurality of distance sensors mounted on or adjacent to the ceiling of the cargo container, each of the distance signals indicating a distance between a corresponding one of the distance sensors and a surface within the interior space of the cargo container;

(b) determining a load state of the cargo container based on one or more of the plurality of the distance signals;

(c) for each of the distance signals, determining a cargo height value based on the distance between the corresponding distance sensor and the surface located within the corresponding cargo detection area; and

(d) calculating a total volume of the interior space of the cargo container occupied by cargo based on the cargo height values and area values for the portions of the total area of the floor of the cargo container in which cargo is present.

2. The method of claim 1 wherein:

each of the distance sensors has a field of view, and the plurality of distance sensors are distributed across the ceiling of the cargo container such that their fields of view define a plurality of cargo detection areas distributed across the floor of the cargo container, wherein each cargo detection area corresponds to a portion of a total area of the floor of the cargo container; and

each of the plurality of distance signals indicates a distance between a corresponding one of the distance sensors and a surface located within a corresponding one of the cargo detection areas.

3. The method of claim 2 further comprising calculating how much of the total area of the floor of the cargo container is occupied by cargo based on the distances indicated by the plurality of distance signals.

4. The method of claim 1 wherein each of the plurality of distance signals indicate a distance between a corresponding one of the distance sensors and either a surface of a piece of cargo or the floor of the cargo container.

5. The method of claim 1 wherein the ceiling of the cargo container is disposed at a height above the floor of the cargo container, and wherein the load state determination step comprises comparing the distance to a distance threshold that is less than the height.

6. The method of claim 1 further comprising providing one or more load state indications to a tracker unit mounted on the cargo container, and based on the one or more load state indications, transmitting load state information from the tracker unit to a backend server via a data communication network.

7. An apparatus for detecting cargo within a cargo container that has a ceiling, a floor, and an interior space disposed between the ceiling and the floor, the apparatus comprising:

a plurality of distance sensors configured for mounting on or adjacent to the ceiling of the cargo container, the plurality of distance sensors generating a plurality of distance signals, each of the distance signals indicating a distance between a corresponding one of the distance sensors and a surface within the interior space of the cargo container; and

one or more processors in communication with the plurality of distance sensors, the one or more processors operable to execute instructions to:

generate a load state indication based on one or more of the plurality of distance signals;

for each load state indication, determine a cargo height value based on the distance between the corresponding distance sensor and the surface located within the corresponding cargo detection area; and

calculate a total volume of the interior space of the cargo container occupied by cargo based on cargo height values and area values for the portions of the total area of the floor of the cargo container in which cargo is present.

8. The apparatus of claim 7 wherein

each of the plurality of distance sensors has a field of view,

the plurality of distance sensors are mounted to the ceiling of the cargo container such that their fields of view define a plurality of cargo detection areas distributed across the floor of the cargo container,

each cargo detection area corresponds to a portion of a total area of the floor of the cargo container, and

each of the distance signals indicate a distance between a corresponding one of the distance sensors and a surface located within a corresponding one of the cargo detection areas.

9. The apparatus of claim 7 wherein the one or more processors are operable to execute instructions to calculate how much of the total area of the floor of the cargo container is occupied by cargo based at least in part on the load state indication.

10. The apparatus of claim 7 further comprising one or more sensor modules configured for mounting on or adjacent to the ceiling of the cargo container, each of the one or more sensor modules containing two or more of the plurality of distance sensors, wherein each of the two or more distance sensors in each sensor module has a field of view that is aligned in a different direction from fields of view of other distance sensors in one and the same sensor module.

11. The apparatus of claim 10 wherein the one or more processors are components of the one or more sensor modules.

12. The apparatus of claim 10 wherein multiple sensor modules are distributed across a length of a central portion of the ceiling of the cargo container.

13. The apparatus of claim 10 wherein multiple sensor modules are distributed across a length of the cargo container adjacent to locations at which the ceiling of the cargo container meets a wall of the cargo container.

14. The apparatus of claim 10 wherein:

one or more of the sensor modules are mounted on a door of the cargo container;

the one or more distance sensors contained in the one or more sensor modules mounted on the door each have a field of view directed toward a back wall of the cargo container when the door is in a closed position; and

the one or more distance sensors contained in the one or more sensor modules mounted on the door each have a field of view directed toward the floor of the cargo container when the door is in an open position.

15. The apparatus of claim 10 wherein at least one of the one or more sensor modules contains an accelerometer used to determine an orientation of the at least one sensor module.

16. The apparatus of claim 7 wherein each of the distance signals indicate a distance between a corresponding one of the distance sensors and either a surface of a piece of cargo or the floor of the cargo container.

17. The apparatus of claim 7 wherein the ceiling of the cargo container is disposed at a height above the floor of the cargo container, and wherein the one or more processors are operable to execute instructions to compare the distance to a distance threshold that is less than the height.

18. The apparatus of claim 7 further comprising a tracker unit configured for mounting on the cargo container, the tracker unit operable to generate cargo loading information based on the load state indication, and transmit the cargo loading information from the tracker unit to a backend server via a data communication network.

19. The apparatus of claim 18 wherein the one or more processors are components of the tracker unit.

20. The apparatus of claim 18 wherein the one or more processors are components of the backend server.

21. The apparatus of claim 7 wherein the plurality of distance sensors comprise laser-ranging time-of-flight sensors or ultrasonic sensors.