Infrared detector module for airborne hyperspectral LiDAR: design and demonstration.

Realizing the integrated acquisition and identification of the elevation information and spectral information of the observation target is at the frontier and a future trend of Earth observation technology. This study designs and develops a set of airborne hyperspectral imaging lidar optical receiving systems and investigates the detection of the infrared band echo signal of the lidar system. A set of avalanche photodiode (APD) detectors is independently designed to detect the weak echo signal of  800-900 nm band. The actual radius of the photosensitive surface of the APD detector is 0.25 mm. We design and demonstrate the optical focusing system of the APD detector in the laboratory and obtain that the image plane size of the optical fiber end faces of the APD detector from channel 47 to channel 56 is close to 0.3 mm. Results show that the optical focusing system of the self-designed APD detector is reliable. On the basis of the focal plane splitting technology of the fiber array, we couple the echo signal of  800-900 nm band to the corresponding APD detector through the fiber array and conduct a series of test experiments for the APD detector. Field test results of the ground-based platform show that the APD detectors in all channels can complete the remote sensing measurement of 500 m. The development of this APD detector solves the problem of hyperspectral imaging under weak light signals and realizes the accurate detection of ground targets in the infrared band by airborne hyperspectral imaging lidar.

A Mid-Infrared Quantum Cascade Laser Ultra-Sensitive Trace Formaldehyde Detection System Based on Improved Dual-Incidence Multipass Gas Cell.

Formaldehyde (HCHO) is a tracer of volatile organic compounds (VOCs), and its concentration has gradually decreased with the reduction in VOC emissions in recent years, which puts forward higher requirements for the detection of trace HCHO. Therefore, a quantum cascade laser (QCL) with a central excitation wavelength of 5.68 µm was applied to detect the trace HCHO under an effective absorption optical pathlength of 67 m. An improved, dual-incidence multi-pass cell, with a simple structure and easy adjustment, was designed to further improve the absorption optical pathlength of the gas. The instrument detection sensitivity of 28 pptv (1σ) was achieved within a 40 s response time. The experimental results show that the developed HCHO detection system is almost unaffected by the cross interference of common atmospheric gases and the change of ambient humidity. Additionally, the instrument was successfully deployed in a field campaign, and it delivered results that correlated well with those of a commercial instrument based on continuous wave cavity ring-down spectroscopy (R2 = 0.967), which indicates that the instrument has a good ability to monitor ambient trace HCHO in unattended continuous operation for long periods of time.

Optical system design for a hyperspectral imaging lidar using supercontinuum laser and its preliminary performance.

To meet the urgent need for surveying and mapping using remote sensing instruments, a hyperspectral imaging lidar using a supercontinuum laser is proposed. This novel lidar system can solve the problem of the mismatching of the traditional lidar retrieved elevation data and hyperspectral data obtained by passive imaging instruments. The optical design of the lidar receiving system is described, developed, and tested in this study. An off-axis parabolic mirror is used as the receiving telescope of the system, and a transmissive grating is used to split the received hyperspectral light to each detection channel. A fiber array equipped with a micro-lens is used to guide the split light to the detectors. In practice, several fibers can be coupled to one detector according to the wavelength sensitivity of different objects. A reference laser is used to monitor the possible energy jitter of each transmitted laser pulse in real time. A spectrum calibration of the receiving system is accomplished in the laboratory, and radiation calibration is applied by receiving the backscattered light reflected by a standard white board. The spectral resolution of a single fiber is approximately 3 nm. An outdoor 500-m distance experiment was carried out for green and yellow leaves in day and evening settings. During the experiment, the wavelength of the laser was 460-900 nm. The reflection spectra collected by the lidar system in day and evening were consistent, indicating that the design of the optical receiving system is reliable and can be used for airborne hyperspectral imaging lidar.

Development of a net ozone production rate detection system based on dual-channel cavity ring-down spectroscopy.

A novel system for measuring net photochemical ozone production rates in the atmosphere based on cavity ring-down spectroscopy (OPR-CRDS) was developed. The system consists of two chambers (a reaction chamber and a reference chamber) and a dual-channel Ox-CRDS detector. To minimize the wall loss of Ox in the chambers, the inner surfaces of both chambers are coated with Teflon film. The performance of the OPR-CRDS system was characterized. It was found that even though the photolysis frequency (J value) decreased by 10%, the decrease in the P(O3) caused by the ultraviolet-blocking film coating was less than 3%. The two chambers had a good consistency in the mean residence time and the measurement of NO2 and Ox under the condition of no sunlight. The detection limit of the OPR-CRDS was determined to be 0.20 ppbv/hr. To further verify the accuracy of the system, the direct measurement values of the OPR-CRDS system were compared with the calculation results based on radical (OH, HO2, and RO2) reactions, and a good correlation was obtained between the measured and calculated values. Finally, the developed instrument was applied to obtain the comprehensive field observations at an urban site in the Yangtze River Delta (China) for 40 days, the time series and change characteristics of the P(O3) were obtained directly, and the good environmental adaptability and stability of the OPR-CRDS system were demonstrated. It is expected that the new instrument will be beneficial to investigations of the relationship between P(O3) and its precursors.

Intensive insulin therapy for septic patients: a meta-analysis of randomized controlled trials.

Background. Studies on the effect of intensive insulin therapy (IIT) in septic patients with hyperglycemia have given inconsistent results. The primary purpose of this meta-analysis was to evaluate whether it is effective in reducing mortality. Methods. We searched PubMed, Embase, the Cochrane Library, clinicaltrials.gov, and relevant reference lists up to September 2013 and including randomized controlled trials that compared IIT with conventional glucose management in septic patients. Study quality was assessed using the Cochrane Risk of Bias Tool. And our primary outcome measure was pooled in the random effects model. Results. We identified twelve randomized controlled trials involving 4100 patients. Meta-analysis showed that IIT did not reduce any of the outcomes: overall mortality (risk ratio [RR] = 0.98, 95% CI [0.85, 1.15], P = 0.84), 28-day mortality (RR = 0.66, 95% CI [0.40, 1.10], P = 0.11), 90-day mortality (RR = 1.10, 95% CI [0.97, 1.26], P = 0.13), ICU mortality (RR = 0.94, 95% CI [0.77, 1.14], P = 0.52), hospital mortality (RR = 0.98, 95% CI [0.86, 1.11], P = 0.71), severity of illness, and length of ICU stay. Conversely, the incidence of hypoglycemia was markedly higher in the IIT (RR = 2.93, 95% CI [1.69, 5.06], P = 0.0001). Conclusions. For patients with sepsis, IIT and conservative glucose management show similar efficacy, but ITT is associated with a higher incidence of hypoglycemia.