Micro-MCA electronic Incident Light Sensor

Enabling Representation of Precise Reflectance 

Values for Micro-MCA and Micro-MCA Snap Systems

 
 

The radiation plants reflect may vary due to factors that are completely unrelated to the plant itself.   The incident radiation that lights the scene, for example, can vary due to cloud cover, humidity, time of day, the season, pollution, and dozens of other factors.   The camera that views the scene can have its view altered by its own settings.   Cameras in auto exposure mode, for example, will vary their exposure in order to obtain the best results for the overall picture.  This might indicate a problem where none exist or mask a problem where one does.   

Tetracam's patented Micro-MCA electronic Incident Light Sensor (e-ILSTM) is designed  to overcome precisely these types of remote sensing setbacks.  The e-ILSTM is an optional accessory that is available with all Micro-MCA and Micro-MCA Snap systems.  The device consists of an up-looking imaging sensor that is equipped with a standard 16 GB micro SD image memory, a fast USB 2.0 interface, a single Mini-MCA 1280 x 1024 CMOS sensor and 8.0 mm filters, each with the same center wavelength and bandwidth values as as those present in the down-looking Micro-MCA.  The filters are contained beneath a translucent lens that diffuses incoming radiation.  The e-ILSTM is attached to the Micro-MCA by means of an electrical umbilical cable in a position that affords a clear un-obscured view of the sky. The umbilical carries power, ground and a serial trigger signal between the e-ILSTM and the Micro-MCA system.   Extension cables are available for mounting the e-ILSTM up to seven meters away from the Micro-MCA system. 

The job of the  e-ILSTM is to gather down-welling radiation at the same wavelengths as the up-welling reflected radiation captured by the Micro-MCA.   The  e-ILSTM saves a calibration image of the sky at the same time that the Micro-MCA master camera signals all of the other cameras in the array to capture images.  Once the mission is completed, the calibration images can be extracted from the  e-ILSTM over the device's USB 2.0 connection or by physically removing the 16 GB micro SD image memory from the e-ILSTM camera.  When processed by Pixelwrench2, every pixel in every image in the array will have two values to process; the reflected value from the objects in the scene and the e-ILS calibration value.   Comparing the two enables the software to represent each pixel by the exact fraction of radiation that it reflects back to the camera.

The ratio of upwelling reflected radiation to down-welling incident light for each pixel in the image is expressed as some fraction of either 255 for an 8-bit image or 1023 for a 10-bit image. The resulting image accurately represents the reflectance value of the radiation at each pixel in the image.   Images that represent reflectance values typically appear darker than those that are optimized to display best overall image exposure by the user (see example images below).

Reflectance values do not change with changes in incident light because a change in the light that lights the scene changes the scene as well.  Lowering incident light proportionally lowers reflected light and the reflectance value stays the same.  In addition, since the Micro-MCA system's master camera controls exposure of all cameras in the array as well as the  e-ILSTM, despite varying exposure settings reflectance values will remain constant.

Reflectance values more accurately reflect the physical and chemical characteristics of the subject being viewed and are less affected by lighting inconsistencies.  Even though incident light may vary from one day to another, if there is no change in the subject then the ratio of reflected light to incident light will stay the same.  Capturing reflectance values provides a better day-to-day comparison between monitored areas of interest because variations in reflectance values provide a more consistently accurate indication of physical or chemical changes in the reflecting bodies themselves. 

 

Example MCA Image without ILS

Example MCA Image with ILS

The electronic-Incident Light Sensor may be ordered with new Micro-MCA systems or existing Micro-MCA system owners may contact Tetracam, obtain an RMA, ship their Micro-MCA systems to our Chatsworth facility and have an  e-ILSTM added to their system. Contact us for current pricing, availability, and further details.