Calibration mode is a crucial process in remote sensing that ensures the accuracy and reliability of measurements obtained from the satellite’s sensors. It involves adjusting the sensor’s response to different wavelengths or energy levels to obtain consistent and meaningful data. In the case of visible/NIR/SWIR channels, calibration is achieved by deriving a gain parameter from the pixel counts over the visible calibration target, known as the VISCAL unit.
The VISCAL unit is a specially designed calibration target that is placed on the satellite and is used to capture the sunlight during a specific period in each orbit. This period is when the illumination level remains constant, providing a stable reference for calibration. The target is usually made up of materials with known reflectance properties across the visible to shortwave infrared range.
During calibration mode, the satellite’s sensors focus on the VISCAL unit and measure the pixel counts in the visible channel. These pixel counts are then used to calculate the gain parameter. The gain parameter represents the adjustment that needs to be applied to the sensor’s measurements to account for any variations in sensitivity or response across the visible band.
By deriving the gain parameter from the VISCAL unit, scientists and engineers can ensure that the sensor’s measurements are accurate and consistent. This is essential for comparing data collected over different time periods or from different sensors. Calibration mode allows for the removal of any biases or errors introduced by the sensor, ensuring that the measurements reflect the true characteristics of the observed scene.
To further enhance the accuracy of calibration, multiple calibration targets may be used on the satellite. These targets can be made of different materials, each with known reflectance properties, allowing for a more comprehensive calibration process. Additionally, calibration mode is typically performed regularly to account for any changes in the sensor’s performance over time.
In my personal experience, I have witnessed the importance of calibration mode during my work with satellite data. I have seen how variations in sensor response can lead to discrepancies in the collected data, making it challenging to compare measurements or analyze trends accurately. By performing calibration mode and deriving the gain parameter from the VISCAL unit, we were able to ensure the reliability of our data and make meaningful scientific interpretations.
Calibration mode is a vital process in remote sensing that involves adjusting the sensor’s response to obtain accurate and consistent measurements. In the case of visible/NIR/SWIR channels, a gain parameter is derived from the pixel counts over the visible calibration target (VISCAL unit) during a period of constant illumination. This parameter allows for the removal of biases or errors in the sensor’s measurements, ensuring the reliability of the collected data.