The polarization payload onboard Fengyun-3 precipitation satellite (FY-3G) is the first Polarization and Multi-Angle Imager (PMAI) with a shortwave infrared channel in China. Three spectral bands are equipped with polarizers : 1030 nm, 1370 nm and 1640 nm. For each of these wavelengths, three similar spectral filters are associated with three polarizers, the direction of the first and the third one being at +60° and -60° from the direction of the central one. The three polarization image of the band are obtained from the subsequent detector response. To compensate for the flight lag, the design uses the wedge prism to register the three images together. The satellite adopts an autonomous 180° yaw maneuver control scheme to guarantee the on-orbital performance. In order to solve the problem of polarization channel registration of imager during satellite inverted flight, we developed a set of on-orbit registration algorithms. In order to verify the effect of the registration algorithm during the inverted flight, we used a typical observation scence to perform pre- and post-calibration tests. During the forward flight of the satellite, the cloudbow from polarization channel was obtained by PMAI. However, during the backward flight due to the wrong channel registration between sub-pixels, the rainbow is drowned in noise. After calibrated by the on-orbit registration algorithms in backward flight, the cloudbow come to appear in the 140° scattering angle. Results show that during inverted flight the registration effect is greatly improved, and the accuracy of polarization observation is dramatically enhanced.
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The selection of atmospheric sample profiles is one of the key factors affecting the accuracy of the fast simulation of satellite channels, but the mechanism of the influence has not been conclusively established. In this paper, the mechanism of atmospheric sample profile selection and its contribution in the forward modeling are discussed through the analysis of the role of transmittance predictors in RTTOV model. The CO2 absorption channel at 15 μm in the infrared band of FY-3C IRAS (InfraRed Atmospheric Sounder) is used as the study object, and the IRAS laminar channel transmittance factor is established based on the TIGR43 profile database. The comparison tests between the profile temperature anomaly and simulation accuracy in the cold and warm scenarios show that the root mean square error (RMSE) of the simulation for the IRAS temperature detection channel is 0.2 K when all the profiles are involved in the regression calculation, compared with the simulation results of LBL. Within the detection height range of the selected CO2 detection channels, there is a strong linear correlation between the profile temperature anomaly and the simulation accuracy in the warm scenario due to the higher order residual term in the Taylor expansion, and more significant accuracy improvement can be obtained if the profile with larger temperature anomaly is removed from the forward modeling.
The polarization instrument of Fengyun-3 precipitation satellite is the first Polarization and Multi-Angle Imager (PMAI) with short-wave infrared channel in China, aiming to accurately measure the radiation characteristics of clouds and aerosols in the atmosphere. The accuracy of radiometric measurement is an important technical index of instrument performance, which is of great significance for the inversion of high-precision quantitative parameters of satellite remote sensing. For the non-polarization channel of a polarization imager, polarization is a kind of interference information, and the polarization sensitivity of the instrument needs to be inverted and quantitatively removed to improve the accuracy of radiation calibration. A method of least squares fitting response value of complete linear polarization incident light based on different polarization angles is proposed to measure the polarization sensitivity of the non-polarization channel full field of view. According to the measured polarization rate of each channel and the polarization characteristics of the incident light, the polarization sensitivity of each channel is calibrated based on the polarization calibration model. The results show that the polarization sensitivity of the non-polarization channel shows obvious edge effect, gradually increasing from the center of the focal plane to the edge, and has obvious spectral differences, the smaller the wavelength having the higher the polarization sensitivity. The maximum polarization sensitivity occurs in the edge field of view of the non-polarization channel in the 1030nm band, close to 1.6%, which has a great impact on the accuracy of radiometric calibration. After polarization sensitivity calibration, the polarization sensitivity of the edge field of view is within 0.5%. The results show that by calibrating the polarization sensitivity of the full field of view of the non-polarization channel, the radiometric calibration can be effectively improved, which provides strong support for high-precision quantitative remote sensing.
The infrared (IR) benchmark sounder is designed to detect the tiny change of long-term global climate by measuring the spectrally resolved IR radiance emitted from Earth to space with high accuracy. Besides, the IR sounder also serve as a space-borne radiometric reference to convert the international fleet of weather sounders into a climate benchmarking system with excellent global coverage and similar measurement accuracy. In order to achieve high accuracy, the benchmark sounder must be tuned to be a linear response system and be well radiometrically calibrated. So the nonlinearity response in an IR detector signal chain needs to be corrected prior to the linear radiometric calibration. There are some algorithmic approaches being commonly used to correct the nonlinear measurements. These methods use the measured nonlinear interferograms to polynomially fit the corrected linear interferograms, without considering the physical root of non-linearity. However, they work well only when the detector nonlinearity is small. Regarding the large nonlinearity, a correction method is proposed in this paper. It follows the nonlinearity response mechanism of the IR detector, and uses the to-be-solved linear interferogram to polynomially fit the measured non-linear interferogram signal formally, and then derive the correction coefficients from the established equations. According to the correction evaluation and methods comparison using the simulated data as proxy measurements, the proposed method is appropriate for both small and large degree of quadratic nonlinearity detectors.
Global outgoing longwave radiation variation is examined for a 6-year (2014-2019) period using reanalysis and FengYun 3B/3C OLR products: the interpolated OLR analyses and the visible and infrared radiometer OLR on FengYun 3 series satellite platforms. Tropical Pacific and Niño key regions are essential range for monitoring El Niño events, which are chosen to investigate the spatial-temporal correlation, seasonal evolution and statistical difference with a variety source of OLR anomalies. Results indicate that monthly OLR anomalies can monitor the Niño variation. OLR anomalies are associated with enhanced amplitude in the EP El Niño, while OLR anomalies exhibit stronger intensity than the CP El Niño index. For FengYun 3B/3C the monthly satellite products have a root mean squared error of 10.94 W/m2 and 12.73 W/m2 as compared for the interpolated OLR products.
Based on spontaneous parametric downconversion process, we propose a novel self-calibration radiometer scheme which can self-calibrate the degradation of its own response and ultimately monitor the fluctuation of a target radiation. Monitor results were independent of its degradation and not linked to the primary standard detector scale. The principle and feasibility of the proposed scheme were verified by observing bromine–tungsten lamp. A relative standard deviation of 0.39 % was obtained for stable bromine–tungsten lamp. Results show that the proposed scheme is advanced of its principle. The proposed scheme could make a significant breakthrough in the self-calibration issue on the space platform.
Duhuang site has been selected as China Radiation Calibration Site (CRCS) for Remote Sensing Satellite Sensors since 1996. With the economic development of Dunhuang city, the ambient of the radiation calibration field has changed in recent years. Taking into account the key role of aerosol in radiometric calibration, it is essential to investigate the aerosol optical properties over Dunhuang radiometric calibration site. In this paper, the CIMEL sun photometer (CE-318) and Mie-scattering Lidar are simultaneously used to measure aerosol optical properties in Dunhuang site. Data from aerosol-bands of sun photometer are used in a Langley method to determine spectral optical depths of aerosol. And Lidar is utilized to obtain information of vertical profile and integrated aerosol optical depths at different heights. The results showed that the aerosol optical depth at 500 nm wavelength during the in-situ measurement campaigns varied from 0.1 to 0.3 in Dunhuang site. And the observation results also indicated that high aerosol concentration layer mostly located at the height of about 2~4 km. These results implies that the aerosol concentration of atmosphere in Dunhuang was relatively small and suitable for in-flight calibration for remote sensing satellite sensors.
The National Satellite Meteorological Center (NSMC)/CMA global sea surface temperature (SST) data are derived from
measurements made by the Visible and Infrared Radiometer (VIRR) on board the FY-3 series polar orbiting satellites.
Quality controlled in situ data from iQUAM (STAR/NESDIS/NOAA) is used in FY-3B/C VIRR matching procedure.
The monthly matchup database (MDB) is created from FY-3C VIRR measurements paired with coincident SST
measurements from buoys since November 2013. The satellite sensor’s brightness temperature and buoy SST pairs are
included in the MDB if they are coincident within 3km in space and 1 hour in time. Least-Square Regression is used for
estimating the first-guess coefficient and SST residuals. Outliers are removed using Median±2STD, and the final
coefficients of robust regression are estimated. A set of SST regression formalisms are tested base on NOAA-
19/AVHRR 2010 MDB. The test shows that, for daytime split-window nonlinear SST (NLSST) is the best, for nighttime
triple-window MCSST (TCSST) is the best, which is agree with STAR/NESDIS’s. The same regression analysis method
also used on FY-3C/VIRR MDB. Compare with the three daytime SST algorithms and five nighttime SST algorithms,
the best algorithm to retrieve FY-3C/VIRR SST for daytime is NLSST and for nighttime is TCSST. Compare with the
coefficients of nighttime algorithm TCSST, it shows that for FY-3B/C VIRR SST, the contribution of 3.7μm band is
smaller than split-window bands. The performance of 3.7μm band of FY-3C/VIRR is better than FY-3B/VIRR, but
worse than NOAA-19/AVHRR.
Medium Resolution Spectral Imager (MERSI) is the key imaging sensor on board Fengyun-3 (FY-3), the second generation polar-orbiting meteorological satellites in China, currently operating on both FY-3A, FY-3B and FY-3C satellites. It has 20 spectral bands, including 19 reflective solar bands (RSBs) with center wavelengths from 0.41μm to 2.1μm and 1 thermal emissive band (TEB) with center wavelength 12μm, making observations at two spatial resolutions: 250 m (bands 1-5) and 1km (bands 6-20). The FY-3C has been launched in 23, Sept., 2013. The MERSI doesn't carry on-board calibration standards. To obtain RSBs radiometric responses, pre-launched field radiometric calibration test which is called Solar Radiation Based Calibration(SRBC) was taken in Dali in 27, Feb. to 2, Mar., 2013. For the SRBC measurement which the sun was the source of irradiance, MERSI viewed the reflected solar irradiance from a set of the sixteen reference spectral on panels with different reflective level. The uniformity, reflectivity and BRDF (Bidirectional reflection of distribution function) of sixteen reference panels were tested in advance. There are two kinds of calibration coefficient generation methods used in SRBC. One is similar as the Sea-WiFS pre-launch calibration method by Langley calibration. Besides this, we use a portable spectrometers produced by Analytical Spectral Devices inc. (ASD inc.) named FieldSpec 3 to measure the absolutely reflected radiance simultaneously. The calibrated spectrometers measured radiance could be as the reference radiance and the the calibration coefficient of the MERSI can be calculated. We called this method Calibration Based on Reference Instrument(CBRI). The results of these two methods are comparable. The CBRI results are less then 6% difference with Langley calibration method in most channels except water-vapor channels and channel 15. An non-linear feature of the most FY-3C/MERSI detectors was found for the first time. This phenomenon is even more obvious for the water-vapor channels. The second order coefficient determined by pre-launched calibration is quite useful to improve the on-obit calibration accuracy.
Intercalibration against a well-calibrated instrument at Low Earth Orbit (LEO) is a common method which has been widely used to assess the in-flight calibration of a new instrument. Different instruments on LEO spacecraft with similar spectral channels can be compared with each other using their simultaneous nadir observations (SNO). The postlaunch calibrations of Medium Resolution Spectral Imager (MERSI) and the Visible Infrared Radiometer (VIRR) in visible channels which are two major multi-spectral imaging radiometers onboard FY-3C are addressed based on SNO intercalibration method. Collection 6 reflectance products of AQUA MODIS are used as reference. The spectral difference impacts of matching channels are simulated and adjusted using GOME-2 hyperspectral measurements. As monitoring the stability of monthly forcing fits, it is found the linear fitting slopes of MERSI VIS channel 1~12 are scene reflectance dependence with relative differences greater than 20%, while the monthly forcing fits of VIRR show well agreement in VIS channels. This is proved to attribute to the nonlinear response of MERSI as the monthly measurements cover different dynamic ranges. A new radiometric calibration equation considering nonlinear correction is proposed based on an on orbit linear adjustment to prelaunch quadratic calibration. The new calibrations are more consistent with SNO samples, and greatly improve the performance over high reflective scene comparing with linear results verified by statistical measurements over Deep Convective Clouds targets. It is demonstrated that other reference is necessary in ocean color channels as MODIS reflectance is within 10% where the nonlinear feature is likely much serious. It is an invaluable lesson that the temporal variation of calibration slope not always indicates the detector’s degradation, but maybe is the valuable information that helps to expose undiscovered characters of instrument.
FY-3C/MERSI has some remarkable improvements compared to the previous MERSIs including better spectral response function (SRF) consistency of different detectors within one band, increasing the capability of lunar observation by space view (SV) and the improvement of radiometric response stability of solar bands. During the In-orbit verification (IOV) commissioning phase, early results that indicate the MERSI representative performance were derived, including the signal noise ratio (SNR), dynamic range, MTF, B2B registration, calibration bias and instrument stability. The SNRs at the solar bands (Bands 1–4 and 6-20) was largely beyond the specifications except for two NIR bands. The in-flight calibration and verification for these bands are also heavily relied on the vicarious techniques such as China radiometric calibration sites(CRCS), cross-calibration, lunar calibration, DCC calibration, stability monitoring using Pseudo Invariant Calibration Sites (PICS) and multi-site radiance simulation. This paper will give the results of the above several calibration methods and monitoring the instrument degradation in early on-orbit time.
The purpose of this study is to select a suitable ocean wind inversion method for FY-3C (MWRI). Based on the traditional empirical model of sea surface wind speed inversion, and in the case of small sample size of FY-3C satellite load regression analysis, this paper analyzes the channel differences between the FY-3C satellite microwave radiation imager (MWRI) and TMI onboard the TRMM. The paper also analyzes the influence of these differences on the channel in terms of receiving temperature, including channel frequency f, sensitivity ΔK and scaling precision K. Then, the limited range of new model coefficient regression analysis is determined, the regression methods of the finite field are proposed, and the empirical model of wind speed inversion applicable to MWRI is obtained, The method corrected by 2014 FY3C observation data and buoy data, and then by anti-electromagnetic interference geostationary communications satellite designed to fit in the FY-3C (MWRI). which achieves strong results. Compared to the TAO buoy data, the RMS of the new model is 1.18 m/s. In addition, the schematic diagram of the global ocean surface wind speed inversion is provided.1
A recently developed 220GHz incoherent radar has potential for remote sensing of low reflectivity atmosphere targets in
Cloud Chamber. Stepped frequency system is used and bandwidth 10GHz. Preliminary reflectivity measurements of
clouds for ranges between 0.2m~4m in narrow Cloud Chamber. The instrument is briefly described. Highlighting
uncertainties due to highly variable attenuation and signal interference. Then the results of investigations of the
transmitter, receiver, Antennas, as well as the atmospheric Propagation Effects are presented. The results of this effort
demonstrate that the radar is a stable, sensitive, system capable of providing accurate power for clouds.
The objective of this study was to integrate the advantages of multi-source remote sensing to
monitor dust storms and better discriminate between regions where dust storms occur. Firstly, The
traditional evidence theory algorithm was improved by not only considering the certainty of the
evidence, but also considering the average level of support for the subsets of evidence in the
discrimination framework in the process of evidence combination by reducing the conflict between
synthesized data. Then the algorithm is applied to the FY-2E infrared difference dust index (IDDI)
and the FY-3A dust strength index (DSI) to categorize the study region as either a dust storm area,
non-dust storm area, or possible dust storm area. Finally, the result was validated and analyzed using
the monitored data from ground stations. Both the accuracy and reliability of the dust monitoring
results were considerably improved using our method.
This study introduces the construction of the satellite observation cycling assimilation system in national satellite
meteorological center (NSMC). A typhoon case (1209 Saola ) is chosen to be performed as a testing experiment to check
the operation of the cycling assimilation, with a low resolution . Three experiments are designed: control, ATOVS
microwave observation assimilation and forecasting with cold starting, assimilation and forecasting with warm starting.
Compared with the cold start forecasting, cycling forecasting showed advance in describing more information of the
Tropical Cyclones in detail. As for track and intensity prediction, both the two assimilation experiments were prior to
control experiment. Especially, the cycling experiment is better than cold experiment in the first one day and third day
and the day before landing, but not act well in its peak period, which may suggest that the model couldn’t not match the
description of the typhoon Saola at the full developing period or upgrading develop period, with the low resolution in the
testing experiments, but also can demonstrate well when it develop slowly or in a relatively steady period.
Retrieval of atmospheric profiles from the vertical atmospheric sounding suite aboard the Chinese
FY-3A satellite has been investigated. A statistical retrieval approach is used to generate atmospheric
temperature and moisture profiles. The statistical retrieval method is only applied to the clear-sky
simulated radiances, achieving good retrieval accuracy. For example, in the simulated experiment, the
retrieved atmospheric temperature and moisture profiles show good agreement with independent
atmospheric samples. The RMS is about 1.2K on the average for temperature profile. The RMS is large
for the near surface levels. The RMS of moisture profile is approximately 11%. The temperature and
moisture fields agree well with the NWP analyses of NCEP.
Field experiments with man-made fires in a forest were conducted to verify fire warning products from satellite remote sensing techniques and to select more effective channels for producing these products. Pine branches and trunks as well as other woods were burned at a designated place in a pine-dominated forest to simulate wild forest fires when a satellite was passing over the sky. Infrared spectral irradiances, visible spectrum, brightness, and temperature were measured concurrently with satellite data at the ground using a medium and near-infrared MOMEM MR154 FT-Spectroradiometer, an infrared thermal imager, and a visible and near-infrared spectroradiometer (ASD FR). The measurements showed two emission peaks in middle infrared band that corresponded exceptionally to the combustion strength. One of the spikes at 4.17 μm reflected the CO emission peak. The other peak spanned through the wavelengths of 4.34-4.76 μm, which exhibited a much stronger response to the fire than the commonly used channel 3.5-4.0 μm for fire monitoring in remote sensing. The results suggest that the wave band 4.34-4.76 μm is probably more sensitive and more effective than the common-used channel for wild fire monitoring using satellite remote sensing techniques. However, the peak of this wavelength band drifted during the burning process, which should be taken into account in channel selection. This band is suitable to determine forest fires. Further studies are needed to use it for retrieving fire strength quantitatively.
Sensitivity studies of atmospheric temperature and humidity profile retrieval from EOS AQUA/AIRS measurements , that involve spectral coverage sensitivity , channel coverage sensitivity , additional predictors effect , are performed via empirical orthogonal function (eigenvectors of covariance ) expansion , leading to the revealment of new features of high-resolution infrared sounding . Simulation studies on atmospheric temperature profile retrieval based on the channel characteristics and spectral response function of IRAS had also be done In order to investigate the performance of InfRared Atmospheric Sounder (IRAS) which will be onboard the FY-3A satellite.
With a fast yet accurate infrared radiation transfer model KCARTA, transmittance, radiance and brightness temperature spectra of top of atmosphere (TOA) over thermal infrared region (605-2805cm-1) was simulated. In simulation, the effects of different spectral resolution, response function shape, spectral calibration accuracy, propagation path and surface emissivity were taken into account. The results from forward calculations show: 1) Improvement of spectral resolution changes the probability of present brightness temperature so that more brightness temperature can be observed. Increased observed brightness temperature guarantee atmospheric sounding with better vertical resolution. 2) A small change in response function, spectral calibration, propagation path or surface emissivity will lead in much larger difference on observed brightness temperature for hyperspectral sounding than for low spectral resolution sounding. Therefore, hyperspectral sensor requires more sensitive SNR. Otherwise, the improvement of sounding will be limited. Results here can be taken as a reference in designing future hyperspectral IR sounder and retrieval algorithm.
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