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Hyperspectral detection of the change rate of organic matter content in agricultural remote sensing requires a high signal-to-noise ratio (SNR). However, due to the large number and efficiency limitation of the components, it is difficult to improve the SNR. This study uses high-efficiency convex grating with a diffraction efficiency exceeding 50% across the 360-850 nm range, a back-illuminated Complementary Metal Oxide Semiconductor (CMOS) detector with a 95% efficiency in peak wavelength, and silver-coated mirrors to develop an imaging spectrometer for detecting soil organic matter (SOM). The designed system meets the spectral resolution of 10 nm in the 360-850 nm range and achieves a swath of 100 km and a spatial resolution of 100 m at an orbital height of 648.2 km. This study also uses the basic structure of Offner with fewer components in the design and sets the mirrors of the Offner structure to have the same sphere, which can achieve the rapid adjustment of the co-standard. This study performs a theoretical analysis of the developed Offner imaging spectrometer based on the classical Rowland circular structure, with a 21.8 mm slit length; simulates its capacity for suppressing the +2nd-order diffraction stray light with the filter; and analyzes the imaging quality after meeting the tolerance requirements, which is combined with the surface shape characteristics of the high-efficiency grating. After this test, the grating has a diffraction efficiency above 50%, and the silver-coated mirrors have a reflection value above 95% on average. Finally, the laboratory tests show that the SNR over the waveband exceeds 300 and reaches 800 at 550 nm, which is higher than some current instruments in orbit for soil observation. The proposed imaging spectrometer has a spectral resolution of 10 nm, and its modulation transfer function (MTF) is greater than 0.23 at the Nyquist frequency, making it suitable for remote sensing observation of SOM change rate. The manufacture of such a high-efficiency broadband grating and the development of the proposed instrument with high energy transmission efficiency can provide a feasible technical solution for observing faint targets with a high SNR.
RESUMO
INTRODUCTION: Despite the widespread provision of free contraceptives and post-abortion care (PAC) services, China grapples with a high rate of unintended pregnancies and subsequent abortions. We aimed to study the evolving characteristics of women seeking abortion and their contraceptive practices before and after abortions, to shed light on the optimisation of Chinese PAC services. METHODS: This study utilised data from an abortion cohort between 2019 and 2021. We studied their demographic features, contraception and abortion histories, reasons and choices using chi-square or linear-by-linear tests. We also explored the potential impact of receiving services at PAC facilities on post-abortion contraception use and repeat abortions using logistic regression models. RESULTS: Among the 9005 participants, 43.4% experienced repeat abortion, without a discernible trend over the 3 years. Noteworthy increases were observed in the percentages of college students (from 1.7% to 6.6%, p<0.01) and middle-aged women (from 23.2% to 26.8%, p<0.01) seeking abortions. Surgical abortion was chosen by nearly 90% of participants with a continuously increasing trend (p trend <0.01). Nearly half of the participants experienced unintended pregnancies due to non-use of contraception. Of the remainder, the majority preferred less or the least effective methods both before and after abortion. Women residing in moderate-gross domestic product (GDP) regions faced a higher risk of repeat abortions (OR 1.33, 95% CI 1.16 to 1.54). Despite this, high-quality PAC services may encourage the use of reliable contraceptive methods, with 86.8% of women changing from least effective or no methods to (most) effective methods post-abortion, and prevent repeat abortions (OR 0.65, 95% CI 0.56 to 0.75). CONCLUSIONS: Increased proportions of college students and middle-aged multiparous women seeking abortions were observed, together with inappropriate preferences for less effective contraception and increasing choice of surgical abortions. Future research should extend the focus to cover the entire abortion period, advocate the rational selection of contraceptive methods, and emphasise the specified PAC services tailored to different socioeconomic groups.