The Research Of Radiometric Calibration Source Based On LED Arrays

The laboratory radiometric calibration is an important tache during thedevelopment of optical remote sensing instruments and it’s effect is to build theresponse function between input radiance and output electric signal. The principle ofradiometric calibration is following full aperture, full field of view and end to end.The extend radiometric source is the standard source of laboratory radiometriccalibration and is required to illuminate the camera with full aperture and full field ofview, so it must have large hatch diameter and ideal cosine radiation performance.The integrating sphere with large caliber is the recognized extend radiometric sourcebecause it is the ideal extend source with good uniformity and diffusion. With thefast development of space optics, the resolution and aperture of space optical remotesensor is larger and larger, which needs the diameter of integrating sphere is biggerand bigger, while causing the multiplied increasing of making difficulty and cost,further more, the moving is difficult while need outfield calibration, so it has becomean extremely urgent task to research a new calibration source with small size andlight weight while satisfying the requirement of uniformity and diffusion.In this paper, the LED arrays was used to substitute the integrating sphere as theradiometric calibration light source, in order to meet the requirement of radiometriccalibration of the optical sensors with large aperture. Compared with theconventional radiometric calibration light source, the LED arrays are small involume, light in weight, low in power, and easily moving. The size of the arrays can be stitched flexibly according to the aperture of the optical remote sensor.This thesis analyzed the characteristics of the calibration light source and statedthe feasibility of LED arrays used as the calibration light source. Illuminationuniformity of LED arrays is studied by theoretical derivation and computingsimulation. The spatial angle distribution and plane illuminance distribution isanalyzed. The viewing angle, arrangement, arrangement of space and other factorson the impact of lighting uniformity is simulated using MATLAB.A source modelof LED arrays is designed based on the requirement on illumination uniformity oflaboratory radiometric calibration. The illumination uniformity of the model issimulated by LightTools and the result indicates that the LED arrays irradianceuniformity is95.1%and the spatial angle radiation uniformity is98.2%. LM3409HVchip is used to achieve analog dimming and microcontroller is used to adjust theLED drive current by controlling input analog voltage to achieve the purpose ofregulating the brightness of light. By analyzing the optical performance parametersof LED, LEDs is tested and filtered to produce arrays light source. The brightness,uniformity, spectrum, color coordinates and other optical parameters is tested. Thetesting results show that: the radiance can be adjusted to achieve different levels; theirradiance uniformity is95.49%, which is consistent with simulation results; and thespatial angle radiation uniformity is94.2%, which have some differences withsimulation results. Finally, based on the analysis of experimental data, this paperindicates that the reasons produce differences between test results and simulationvalue is that the consistency of the LEDs is not100%, the diffusion properties of thematerial is not to meet the ideal cosine radiation performance, while themeasurement error in the testing process is inevitable.