Dynamic Range Extending Method For Push-broom Space Remote Sensing Cameras

As one of the important means of earth observation,space remote sensing cameras play an irreplaceable role in both residential areas(such as geographical plotting,land and resources management,weather forecast,etc.)and military field(such as battlefield surveillance,damage assessment,etc.).With the development of science and technology,the temporal resolution,spatial resolution and wavelength resolution of remote sensing cameras as well as their signal-to-noise ratio and modulation transfer function are improved greatly.However,in terms of remote sensing cameras,an important indicator is the dynamic range which is limited by factors,such as full-well capacity of the image sensors.Meanwhile,the dynamic range is generally between 60 dB and 80 dB,and is much lower than that of the natural scenes(which could reach 200dB).In addition,owing to special imaging modes,the traditional HDR imaging method cannot be applied to space remote sensing imaging field.For all the above reasons,proceeding from the engineering practice and focusing on dynamic range(thereafter DR)extending,this thesis puts forward four relevant solutions to push-broom remote sensing cameras with different imaging methods.Specifically speaking,this thesis mainly includes the following four points:1)The dynamic range extending method based on setting double TDI stages is proposed;and it can be applied to push-broom space remote sensing cameras with DTDI imaging technology.This method adopts a digital-domain time-delay-integration imaging technology,aiming at obtaining two images with different exposure time for the same scene one time;and then by the image fusion technology,the dynamic range can be extended.As expected,the dynamic range extension could be 26.02 dB by experimentations.2)The dynamic range extending method based on the DTDI technology with fixed TDI stage is proposed;and it can also be applied to push-broom space remote sensing cameras with DTDI technology.By giving a high value to the TDI stage for DTDI imaging technology,a remote sensing image with a high quantization resolution and high dynamic range can be achieved.Then aided by the selection of display windows,the images can be adapted for show on a conventional 8-bit display.On account of display windows' automatic selection of HDR images,selection criteria are put forward in this chapter.Moreover,focusing on characteristics of the important targets in high-resolution remote sensing images,this chapter proposes a fast and efficient way with the PSO algorithm to select an area with the largest amount of marginal information for evaluation.And this method can improve the image processing efficiency,diminishing the size of hardware and software,lowering the cost and power consumption.3)The DR extending method based on modeling the imaging chain is proposed;and it can be applied to push-broom space remote sensing cameras with multi-spectral TDI CCD detectors.On the basis of panchromatic remote sensing images with big TDI stage and high resolution,this method can obtain an additional image with small TDI stage and high resolution by multi-spectral image fusion and resolution's improvement.Finally,the dynamic range can be extended by HDR image fusion.In these steps,the key is to get a panchromatic image through multi-spectral images' fusion,which is based on the imaging chain model.By theory analyzing and experiments verifying,this method can increase the dynamic range of the multi-spectral push-broom camera by 24.08 dB.4)The dynamic range extending method based on multi-spectral images' PCA transformation is proposed;and it can obtain a panchromatic image with PCA algorithm to make the fusion of multi-spectral images and improve resolution,from the view of keeping the specific information of each band and wiping off redundant information.At the same time,the panchromatic band and multi-spectral bands of TDI CCD will be given different values;and then two images with different exposure time can be obtained.At last,the dynamic range extending of push-broom space remote sensing cameras can be realised through HDR image fusion.Finally,the dynamic range can be increased by 18.06 dB.