System and method for automatic control of exposure time in an imaging instrument
In an embodiment, a computer-implemented method of calibrating an imaging system in real-time, comprising: obtaining a first reading by a first sensor; establishing a dynamic link between the first reading and exposure time of a second sensor; using the dynamic link to control the exposure time of the second sensor; obtaining a second reading by the second sensor during the controlled exposure time; wherein the steps are performed by one or more computing devices.
1. A method of calibrating an imaging system in real-time, comprising:
establishing a dynamic link expressing a proportional relationship between a first reading by a first sensor and an exposure time of a second sensor; and
calibrating the exposure time of the second sensor based on the dynamic link.
2. The method of claim 1 , wherein method is performed using an unmanned aircraft system (UAS) during one UAS mission.
3. The method of claim 2 , comprising obtaining the first reading by the first sensor.
4. The method of claim 3 , wherein obtaining the first reading comprises:
obtaining solar irradiance (Esun min) for a given wavelength at the lowest elevation angle allowed by a light diffuser of the first sensor;
obtaining solar irradiance (Esun max) for the given wavelength at the maximum elevation angle of the one UAS mission;
calibrating exposure time of the first sensor to capture readings between Esun min and Esun max; and
transforming the first reading into an observed solar irradiance (Esun obs).
5. The method of claim 3 , wherein establishing a dynamic link comprises: determining, based on Esun obs, a maximum radiance value (LDetector max) of an array of light detectors of the second sensor; and
determining, based on LDetector max, a maximum irradiance value (EDetector max) of an array of light detectors of the second sensor.
6. The method of claim 5 , wherein the dynamic link is a proportion between Esun obs and EDetector max.
7. The method of claim 6 , wherein calibrating the exposure time of the second sensor based on the dynamic link comprises applying the proportion as a scale to a nominal exposure time of the second sensor.
8. The method of claim 6 , wherein the dynamic link comprises a factor.
9. The method of claim 8 , wherein the factor is a maximum reflectivity of a target (pMax target).
10. The method of claim 1 , wherein the imaging system is coupled with an unmanned aircraft system (UAS).
11. The method of claim 10 , wherein the first sensor is an upwards looking sensor on the UAS and the second sensor is a downwards looking sensor on the UAS.
12. The method of claim 1 , comprising obtaining a second reading by the second sensor during the calibrated exposure time.
13. An imaging system comprising:
a first sensor, a second sensor, and a system control board all communicatively coupled together; and
wherein the system control board is configured to:
establish a dynamic link expressing a dynamic relationship between a first reading from the first sensor and an exposure time of the second sensor; and
calibrate the exposure time of the second sensor based on the dynamic link.
14. The imaging system of claim 13 , wherein communication between the first sensor, the second sensor, and the system control board is provided in real-time during one unmanned aircraft system (UAS) mission.
15. The imaging system of claim 14 , wherein the first sensor is configured to obtain a first reading.
16. The imaging system of claim 15 , wherein the first reading is obtained by: obtaining solar irradiance (Esun min) for a given wavelength at the lowest elevation angle allowed by a light diffuser of the first sensor;
obtaining solar irradiance (Esun max) for the given wavelength at the maximum elevation angle of the one UAS mission;
calibrating exposure time of the first sensor to capture readings between Esun min and Esun max; and
transforming the first reading into an observed solar irradiance (Esun obs).
17. The imaging system of claim 16 , wherein the dynamic link is established by: determining, based on Esun obs, the maximum radiance value (LDetector max) of an array of light detectors of the second sensor; and
determining, based on LDetector max, the maximum irradiance value (EDetector max) of an array of light detectors of the second sensor.
18. The imaging system of claim 17 , wherein the dynamic link is a proportion between Esun obs and EDetector max.
19. The imaging system of claim 18 , wherein the proportion is applied as a scale to a nominal exposure time of the second sensor.
20. The imaging system of claim 18 , wherein the dynamic link includes a factor.
21. The imaging system of claim 20 , wherein the factor is maximum reflectivity of a target (pMax target).
22. The imaging system of claim 13 , wherein the imaging system is coupled with an unmanned aircraft system (UAS).
23. The imaging system of claim 22 , wherein the first sensor is an upwards looking sensor on the UAS and the second sensor is a downwards looking sensor on the UAS.
24. The imaging system of claim 13 , wherein the second sensor is configured to obtain a second reading during the calibrated exposure time.