Solar X-ray and EUV imager on board the FY-3E satellite.

The solar X-ray and Extreme Ultraviolet Imager (X-EUVI), developed by the Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences (CIOMP), is the first space-based solar X-ray and Extreme ultraviolet (EUV) imager of China loaded on the Fengyun-3E (FY-3E) satellite supported by the China Meteorological Administration (CMA) for solar observation. Since started work on July 11, 2021, X-EUVI has obtained many solar images. The instrument employs an innovative dual-band design to monitor a much larger temperature range on the Sun, which covers 0.6-8.0 nm in the X-ray region with six channels and 19.5 nm in the EUV region. X-EUVI has a field of view of 42', an angular resolution of 2.5″ per pixel in the EUV band and an angular resolution of 4.1″ per pixel in the X-ray band. The instrument also includes an X-ray and EUV irradiance sensor (X-EUVS) with the same bands as its imaging optics, which measures the solar irradiance and regularly calibrates the solar images. The radiometric calibration of X-EUVS on the ground has been completed, with a calibration accuracy of 12%. X-EUVI is loaded on the FY-3E satellite and rotates relative to the Sun at a uniform rate. Flat-field calibration is conducted by utilizing successive rotation solar images. The agreement between preliminarily processed X-EUVI images and SDO/AIA and Hinode/XRT images indicates that X-EUVI and the data processing algorithm operate properly and that the data from X-EUVI can be applied to the space weather forecast system of CMA and scientific investigations on solar activity.

[The Sun Glint Area Reflectance Calculation of VIIRS Middle Infrared Channel in South Indian Ocean Based on Improved Nonlinear Split Window Model].

The energy received through remote sensing sensors contains the amount of reflected solar energy and emitted energy of objects in middle-wave infrared (MWIR, 3~5 µm). Usually, the reflected solar energy is weak in MWIR spectrum. In some certain situations like sun glint area in sea surface, however, the energy is relatively significant and less sensitive to atmospheric effects. Meanwhile, for the satellite sensor which equipped with onboard calibration system, its onboard radiation performance of MWIR(using blackbody calibration)is quite stable. Therefore, the MWIR reflectance in sea surface glint area can be considered as a reference for cross-calibration between the solar reflected bands. Based on this idea, this paper constructed an improved non-linear split window model that is suitable for VIIRS (visible infrared imaging radiometer) MWIR band and used this model to calculate the MWIR reflectance of sun glint area in southern Indian Ocean. This model made statistics, getting the relationship between the reflectance of VIIRS M12 and M13 bands at first, and then used the non-linear split window algorithm to calculate the actual sea surface reflectance. The uncertainty of the simulation model was 0.83%. On this basis, this paper calculated sea surface reflectance of selected sample regions based on the data of VIIRS M12 band (center wavelength: 3.697 µm) in sun glint areas. And then verified the reflectance accuracy by two methods, getting the two accuracies were about 0.239% and 0.23%, respectively. It proves that the calculation model in this paper can greatly improve the accuracy compared to the situation when the sea surface reflectance is between M12 and M13 which are assumed to be equal (accuracy of 2.48% and 1.03%, respectively). It also indicated that the model is feasible and effective to calculate the reflectance in sea surface glint area with VIIRS M12 MWIR band, and the accuracy can meet the requirements of MWIR sea surface reflectance as a calibration reference among bands.

[Study on Orbit Radiometric Calibration for FY-2 Visible Band based on Deep Convective Cloud].

A radiometric calibration method is described in this paper by using the deep convective clouds (Deep Convective Cloud, DCC) target for FY-2 visible channel. The deep convective cloud can be used as the radiometric calibration transfer object. The on-operational FY-2 radiometric calibration bias and the long-term degradation trend are evaluated according to the AQUA/MODIS instrument as the baseline of radiometric reference and DCC. The results show that: (1) There are different degrees of degradation for FY-2D, FY-2E and FY-2F, among which FY-2D has the biggest degradation due to the longest period. The annual rates of degradation for FY-2D and FY-2E are quite similar, 1.67% and 1.69% respectively, whereas the rate for FY-2F is lower with 0.81%; (2) During the period of satellite eclipse, the instruments are not stable and this phenomenon could be detected by the DCC method;(3) There are bias in the the operational radiometric calibration between FY-2 and AQUA/MODIS, which is treated as the the radiometric reference usually. The radiometric calibration method based on DCC could work well in the radiometric calibration for FY-2. The results will help us to understand the degradation of instrument and for quantitative application usage.

[On-orbit radiometric calibration accuracy of FY-3A MERSI thermal infrared channel].

Accurate satellite radiance measurements are significant for data assimilations and quantitative retrieval applications. In the present paper, radiometric calibration accuracy of FungYun-3A (FY-3A) Medium Resolution Spectral Imager (MERSI) thermal infrared (TIR) channel was evaluated based on simultaneous nadir observation (SNO) intercalibration method. Hyperspectral and high-quality measurements of METOP-A/IASI were used as reference. Assessment uncertainty from intercalibration method was also investigated by examining the relation between BT bias against four main collocation factors, i. e. observation time difference, view geometric difference related to zenith angles and azimuth angles, and scene spatial homogeneity. It was indicated that the BT bias is evenly distributed across the collocation variables with no significant linear relationship in MERSI IR channel. Among the four collocation factors, the scene spatial homogeneity may be the most important factor with the uncertainty less than 2% of BT bias. Statistical analysis of monitoring biases during one and a half years indicates that the brightness temperature measured by MERSI is much warmer than that of IASI. The annual mean bias (MERSI-IASI) in 2012 is (3.18±0.34) K. Monthly averaged BT biases show a little seasonal variation character, and fluctuation range is less than 0.8 K. To further verify the reliability, our evaluation result was also compared with the synchronous experiment results at Dunhuang and Qinghai Lake sites, which showed excellent agreement. Preliminary analysis indicates that there are two reasons leading to the warm bias. One is the overestimation of blackbody emissivity, and the other is probably the incorrect spectral respond function which has shifted to window spectral. Considering the variation character of BT biases, SRF error seems to be the dominant factor.

[On-orbit response variation analysis of FY-3 MERSI reflective solar bands based on Dunhuang site calibration].

MERSI is the keystone payload of FengYun-3 and there have been two sensors operating on-orbit since 2008. The on-orbit response changes obviously at reflective solar bands (RSBs) and must be effectively monitored and corrected. However MERSI can not realize the RSBs onboard absolute radiometric calibration. This paper presents a new vicarious calibration (VC) method for RSBs based on in-situ BRDF model, and vector radiometric transfer model 6SV with gaseous absorption correction using MOTRAN. The results of synchronous VC experiments in 4 years show that the calibration uncertainties are within 5% except for band at the center of water vapor absorption, and 3% for most bands. Aqua MODIS was taken as the radiometric reference to evaluate the accuracy of this VC method. By comparison of the simulated radiation at top of atmosphere (TOA) with MODIS measurement, it was revealed that the average relative differences are within 3% for window bands with wavelengths less than 1 microm, and 5% for bands with wavelengths larger than 1 microm (except for band 7 at 2.1 microm). Besides, the synchronous nadir observation cross analysis shows the excellent agreement between re-calibrated MERSI TOA apparent reflectance and MODIS measurements. Based on the multi-year site calibration results, it was found that the calibration coefficients could be fitted with two-order polynomials, thus the daily calibration updates could be realized and the response variation between two calibration experiments could be corrected timely; there are large response changes at bands with wavelengths less than 0.6 microm, the degradation rate of the first year at band 8 (0.41 microm) is about 14%; the on-orbit response degradation is maximum at the beginning, the degradation rates slow down after one year in operation, and after two years the responses even increase at some band with wavelengths larger than 0.6 microm.

[Roles of glucosinolates in the interrelationships between Brassicaceae plants and insects: a review].

Glucosinolates (GS) are the important secondary metabolites of Brassicaceae plants, playing an important role in regulating the interrelationships between Brassicaceae plants and insects. GS can protect Brassicaceae plants against euryphagous herbivorous pests because of the toxicity of GS and their breakdown products. However, oligophagous pests which have evolved manifold metabolic pathways to cope with the defensive compounds depended fully on GS and their volatile breakdown products for host-plant recognition and orientation. The GS ingested by herbivores are also toxic to carnivores, and can directly deter predators. On the other hand, predators and parasitoids are attracted by the volatile breakdown products of GS from the Brassicaceae plants damaged by herbivores. Based on the recent findings, this paper reviewed the defensive function of GS against herbivores, host selection of oligophagous pests, GS metabolic pathways of herbivores, induction of GS by herbivores, and effects of GS on the third tropic level. Future directions and techniques in this research field were also suggested.

[New method study of sites vicarious calibration for SZ-3/CMODIS].

Chinese MODIS onboard ShenZhou-3 spacecraft (SZ-3/CMODIS)is the experiment instrument of next generation environmental and meteorological satellites. CMODIS can obtain the data of 30 bands in visible and near infrared region from the earth-atmosphere system. But the quantitative application of these data is limited by radiometric calibration The present paper addresses a new concept of semi-synchronous measurements with satellite observation based on the traditional sites vicarious calibration It can meet the expected calibration requirement under the condition of no enough ground measurements. In addition to this, the reflectance of Dunhuang Calibration site is very smooth on the Vis-NIR spectral region A new cross-calibration was also conducted experimentally using the spectral interpolation of atmospheric correction reflectance from EOS/MODIS. The results of these two methods were compared and verified with each other and showed that they are effective and reliable. These new radiometric calibration methods provide good technique experiences for the next generation in-flight optical sensors.

[Field measurement of Gobi surface emissivity spectrum at Dunhuang calibration site of China].

Gobi surface emissivity spectrum of Dunhuang radiometric calibration site of China is one of the key factors to calibrate the thermal infrared remote sensors using land surface. Based on the iterative spectrally smooth temperature/emissivity separation (ISSTES)algorithm, Dunhuang Gobi surface emissivity spectrum was measured using BOMEM MR154 Fourier transform spectroradiometer and Infrared Golden Board. Emissivity spectrum data were obtained at different time and locations. These spectrum data were convolved with the channel response function of CE312 radiometer and compared with the channel emissivity measured by the same instrument. The results showed that the difference between these two kinds of channel emissivity was within 0.012 and exhibited a good consistency. With these measured emissivity spectra, all of the mainstream thermal infrared remote sensors can be calibrated using Dunhuang Gobi surface at radiometric calibration site of China.