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 computer-implemented method of calibrating an imaging system in real-time, comprising:
under control of stored program instructions executed using a processor, obtaining a first reading by a first sensor;
after the first reading by the first sensor is obtained, establishing, by executing the instructions, a dynamic link expressing a proportional relationship between the first reading and exposure time of a second sensor;
by executing the instructions, using the dynamic link to calibrate the exposure time of the second sensor;
by executing the instructions, obtaining a second reading by the second sensor during the calibrated exposure time;
wherein the method is performed by one or more computing devices.
2. The computer-implemented method of claim 1 , wherein the obtaining the first reading, the establishing, the using, and the obtaining the second reading are performed using a processor of an unmanned aircraft system (UAS) during one UAS mission.
3. The computer-implemented method of claim 2 , wherein the obtaining the first reading includes:
obtaining solar irradiance (E sun min ) for a given wavelength at the lowest elevation angle allowed by a light diffuser of the first sensor;
obtaining solar irradiance (E Sun max ) for the given wavelength at the maximum elevation angle of the UAS mission;
calibrating exposure time of the first sensor to capture readings between E Sun min and E Sun max ;
transforming the first reading into an observed solar irradiance E Sun obs .
4. The computer-implemented method of claim 3 , wherein the establishing includes:
determining, based on E Sun obs , the maximum radiance value (L Detector max ) of an array of light detectors of the second sensor;
determining, based on L Detector max , the maximum irradiance value (E Detector max ) of an array of light detectors of the second sensor.
5. The computer-implemented method of claim 4 , wherein the dynamic link is a proportion between E Sun obs and E Detector max .
6. The computer-implemented method of claim 5 , wherein the using includes applying the proportion as a scale to a nominal exposure time of the second sensor.
7. The computer-implemented method of claim 5 , wherein the dynamic link includes a factor.
8. The computer-implemented method of claim 7 , wherein the factor is maximum reflectivity of a target (ρ Max target ).
9. The computer-implemented method of claim 1 , wherein the imaging system is coupled with an unmanned aircraft system (UAS).
10. The computer-implemented method of claim 9 , wherein the first sensor is an upwards looking sensor on the UAS and the second sensor is a downwards looking sensor on the UAS.
11. An imaging system comprising:
a first sensor, a second sensor, and a system control board all communicatively coupled together;
wherein the first sensor is configured to obtain a first reading;
wherein the system control board is configured to:
after the first reading by the first sensor is obtained, establishing a dynamic link expressing a dynamic relationship between the first reading and an exposure time of the second sensor;
use the dynamic link to calibrate the exposure time of the second sensor;
wherein the second sensor is configured to obtain a second reading during the calibrated exposure time.
12. The imaging system of claim 11 , 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.
13. The imaging system of claim 12 , wherein the first reading is obtained by:
obtaining solar irradiance (E Sun min ) for a given wavelength at the lowest elevation angle allowed by a light diffuser of the first sensor;
obtaining solar irradiance (E Sun max ) for the given wavelength at the maximum elevation angle of the UAS mission;
calibrating exposure time of the first sensor to capture readings between E Sun min and E Sun max ;
transforming the first reading into an observed solar irradiance E Sun obs .
14. The imaging system of claim 13 , wherein the dynamic link is established by:
determining, based on E Sun obs , the maximum radiance value (L Detector max ) of an array of light detectors of the second sensor;
determining, based on L Detector max , the maximum irradiance value (E Detector max ) of an array of light detectors of the second sensor.
15. The imaging system of claim 14 , wherein the dynamic link is a proportion between E Sun obs and E Detector max .
16. The imaging system of claim 15 , wherein the proportion is applied as a scale to a nominal exposure time of the second sensor.
17. The imaging system of claim 15 , wherein the dynamic link includes a factor.
18. The imaging system of claim 17 , wherein the factor is maximum reflectivity of a target (ρ Max target ).
19. The imaging system of claim 11 , wherein the imaging system is coupled with an unmanned aircraft system (UAS).
20. The imaging system of claim 19 , wherein the first sensor is an upwards looking sensor on the UAS and the second sensor is a downwards looking sensor on the UAS.