Signal to Noise Ratio (SNR) is a metric used to link the image quality and radiometric performance of the remote sensing imaging systems. It is one of the remote sensing imaging system's design parameters that represents the image quality. SNR calculation and analysis should be carried out at design phase of remote sensing imaging systems. This calculation and analysis are crucial for confirmation of design success. It is important to show that the light flux reaching the sensor and the generated electrons on sensor is enough to create a high quality image. In this paper, the spectral and total light flux power calculations are presented and SNR analysis in near infrared wavelength region for a remote sensing imaging system used at low earth orbit is demonstrated. Light flux power calculation and SNR analysis are necessary for designing an optical imaging system. The amount of light flux entering to the sensor should be calculated. SNR should also be analyzed to determine the entrance baffle diameter and estimate the image quality of the optical imaging system. The proposed method provides 28.2% electrons filling ratio per pixel, 0.56 V gain and the SNR of 861 for the 2.5 ms operation of the optical system.