Underwater imaging is plagued by light absorption and scattering, resulting in distorted, blurry, and low-contrast. This paper introduces an innovative underwater image restoration algorithm that combines natural lighting-based airlight estimation with the refined dark channel prior. The algorithm directly estimates airlight, considering various underwater conditions such as depth, water quality, and camera-object distance, using the Jaffe-McGlamery underwater image formation model tailored for real-world underwater scenarios. A transmission map formula rooted in the refined dark channel prior is then derived. Finally, the algorithm employs the estimated airlight and transmission map to restore the image. Experimental results validate the algorithm's effectiveness in removing airlight artifacts, enhancing image contrast, and providing a clearer and more natural visual output. This approach promises to advance the quality of underwater imaging and its applicability across various domains.
Based on the MODIS surface reflectance data, the surface reflectance feature database of different surface types in Hefei and Shenyang was constructed in different seasons. First, the normalized difference vegetation index (NDVI) and blue/red light band reflectivity are used to classify the land surface into three categories: vegetation, bare soil, and ice/snow. Feature parameter fitting is performed on different surfaces, and the bidirectional reflectance distribution function (BRDF) feature parameter database is constructed. According to the definition of black sky/white sky albedo, the corresponding band albedo is calculated, and the narrow band and wide band albedo parameter database is also constructed. Analysing the distribution characteristics of BRDF and the change in black-sky/white-sky albedo (BSA/WSA), the results show that the BRDF on the vegetation surface has an obvious hot spot effect. The BSA/WSA of the vegetation is higher than that of the visible band in the near-infrared band, and bare soil, except Hefei in summer, has the same trends. The albedo of the ice and snow surface is significantly higher than that of the other two types of surfaces.
Bioaerosol aerosols originate from a biological source or a biologically active composition in the air everywhere, even in the presence of the ocean and polar regions. Bioaerosols are essential for research in many fields, such as public health safety, botany, and biological warfare. Laser-induced fluorescence technology is a method of using lasers to irradiate a medium so that the electrons in the medium that are originally in equilibrium absorb the photon energy of a specific wavelength and transition to different vibrational energy levels in the excited state, thereby emitting fluorescence of different wavelengths. The wavelength of fluorescence is always longer than the excitation wavelength. In this paper, a bioaerosol detection lidar is developed based on laser-induced fluorescence technology, which can perform fluorescence detection of biological substances at a certain distance, providing a certain basis for real-time detection of bioaerosols. The bioaerosol detection lidar developed in this study provides two laser wavelengths of 266 nm and 355 nm as excitation wavelengths for the detection of two fluorescent substances, tryptophan and riboflavin, contained in bioaerosols. In an outdoor environment, the lidar developed this time was used to verify the detection of tryptophan and riboflavin at different detection distances (30 m, 360 m, 1374 m). After analyzing the detection results, it is concluded that lidar can effectively detect two fluorescent substances, riboflavin and tryptophan, at 30 m, 360 m, and 1374 m.
The spatial parallelism of the receiving and launching optical axis of the atmospheric detection lidar system directly affects the validity of the detection data. The high-precision optical path automatic adjustment system is one of the guarantee conditions for the reliable detection of the space-borne lidar. Common optical path automatic adjustment methods can be divided into echo signal intensity method and spot adjustment method. Based on the Space-borne lidar echo signal intensity adjustment method, fuzzy control is introduced, the tracking error and tracking error change rate is selected as the input of the fuzzy controller, and the output is the system adjustment step size. A variable step size segmentation adjustment algorithm is proposed, and the Turtle library in Python is used for adjustment route tracking simulation. The simulation results show that the stability of the fuzzy control system is higher than that of the traditional method. And randomly selected 1000 sample points, and selected the optimal path adjustment step length in the extremely small range to be 5μrad and 1μrad respectively for comparative analysis. It is found that the minimum range adjustment step size will also affect the stability of the system, and the step size is 5μrad adjustment effect is better.
The gain of the avalanche photodiode (APD) is temperature sensitive, which greatly limits the application of APD for the all-weather operation in field. In this paper, a dual temperature compensation circuit for APD that included temperature control and high voltage compensation was designed. The temperature control part uses MAX1978 for APD proportional-integral-derivative (PID) temperature control through thermistor and thermo electric cooler (TEC), so that APD temperature is kept constant in a certain ambient temperature range. According to general diode‘s temperature characteristics, the high voltage compensation part compensates for the high voltage drift needed to stabilize the gain of the APD when ambient temperature changes, using diode 1N914. This further improves the gain stability of the APD. The dual temperature compensation circuit improves the stability of the APD gain, expands the range of APD's ambient temperature and reduces the thermal noise.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.