High sensitivity is needed for space-based infrared weak target detecting. Pixel-level Digital Integration is an effective method for promoting detection sensitivity. It’s well suited for long integration time or high irradition targets detecting. To meet the application requirements, multistage digital TDI and secondary quantification were proposeed based on pixel-level digital integration. These methods could extend integration time equivalent and restrain quantization noise. The multistage digital TDI could overcome the problem of integral time limited by the dwell time of space-based platform. The secondary quantification could reduce quantization noise to an ignorable level and therefore promote system sensitivity efficiently to photon-noise limit. On this work in progress, detecting systems with milli-kelvin level sensitivity and for infrared weak targets could be carried out.
In this paper, the infrared radiation characteristics of sea background have been studied. First, MODTRAN4.0 was used to calculate the transmittance of mid-infrared and far-infrared, and the solar spectral irradiance, the atmospheric and sea surface radiation. Secondly, according to the JONSWAP sea spectrum model, the different sea conditions grid model based on gravity wave theory was generated. The spectral scattering of the sun and the atmospheric background radiation was studied. The total infrared radiation of the sea surface was calculated. Finally, the infrared radiation of a piece of sea surface was mapped to each pixel of the detector, and the infrared radiation is simulated. The conclusion is that solar radiance has a great influence on the infrared radiance. When the detector angle is close to the sun’s height angle, there will be bright spots on the sea surface.
This paper gives the preprocessing technique research which includes odd-even calibration, bad pixels compensation and non-uniformity calibration for the high sensitivity push-broom long wave infrared camera. The noise equivalent temperature difference (NETD) of the infrared camera has achieved less than 10 mK. The paper analyzes high sensitive imaging effects by using different preprocessing standards according to the test data, also analyzes the effects on imaging quality when using different preprocessing methods. At last the paper gives the suitable image preprocessing methods for the high sensitive infrared camera: the odd-even calibration method considering velocity to height ratio, the bad pixels compensation methods which are unique for temporal and spatial bad pixels and the non-uniformity calibration methods which combines the calibration based on black body testing data and the calibration based on real scene imaging data. It is validated that the residual nonuniformity of the infrared image can be reduced to 0.03% by using the preprocessing methods, which is satisfied for the requirement of high sensitive imaging.
Along with the further application of optical remote sensing, it becomes main trend to realize high spatial resolution, high time resolution, high spectrum resolution and high irradiance sensitivity simultaneously. We present a new satellite-based imaging system that will provide images with these high performances. The structure of the system is compact with small size and light weight. The IR imager, a new generation of high resolution optical remote sensing, is universally acknowledged as the most effective approach to surveil dynamic changes in the environment on the earth. Pushbroom imaging fashion with high efficiency and long-array focal plane detector with passive cooling are adopted to realize area imaging relevant to the flight direction of satellite. The instrument is a dual-optical-path system with long-wave infrared (LWIR) and mid-short-wave infrared (MW-SWIR) bands，which has 4 narrow spectrum bands respectively. An IR dichroic beam-splitter is use to divide wideband incident infrared into LWIR and MW-SWIR. Then two pieces of joint filters, which are integrated in front of detectors and then enveloped by IR Dewars, are used to divide the LWIR and MWIR into 4 spectral bands separately. The focal plane arrays (FPA) are fixed on the optical imaging plane of the lens. The LWIR and MW-SWIR FPA are cooled around 80K or even below. For cooled FPA, optical system must provide a real, accessible exit pupil coupled with a fast f/number refractive component in a Dewar and very close to the FPA. Compared to traditional infrared instruments, high spatial resolution and spectrum resolution can be obtained simultaneously within mass, volume and performance constraints.