scholarly journals Spectral Calibration Algorithm for the Geostationary Environment Monitoring Spectrometer (GEMS)

2020 ◽  
Vol 12 (17) ◽  
pp. 2846
Author(s):  
Mina Kang ◽  
Myoung-Hwan Ahn ◽  
Xiong Liu ◽  
Ukkyo Jeong ◽  
Jhoon Kim
Keyword(s):  
Solar Irradiance ◽  
Spectral Response ◽  
Nonlinear Least Squares ◽  
Reference Spectrum ◽  
Test Results ◽  
Environment Monitoring ◽  
Spectral Calibration ◽  
Sensitivity Tests ◽  
Calibration Algorithm ◽  
Least Squares Approach

The Geostationary Environment Monitoring Spectrometer (GEMS) onboard the Geostationary Korean Multi-Purpose Satellite 2B was successfully launched in February 2020. GEMS is a hyperspectral spectrometer measuring solar irradiance and Earth radiance in the wavelength range of 300 to 500 nm. This paper introduces the spectral calibration algorithm for GEMS, which uses a nonlinear least-squares approach. Sensitivity tests for a series of unknown algorithm parameters such as spectral range for fitting, spectral response function (SRF), and reference spectrum were conducted using the synthetic GEMS spectrum prepared with the ground-measured GEMS SRF. The test results show that the required accuracy of 0.002 nm is achievable provided the SRF and the high-resolution reference spectrum are properly prepared. Such a satisfactory performance is possible mainly due to the inclusion of additional fitting parameters of spectral scales (shift, squeeze, and high order shifts) and SRF (width, shape and asymmetry). For the application to the actual GEMS data, in-orbit SRF is to be monitored using an analytic SRF function and the measured GEMS solar irradiance, while a reference spectrum is going to be selected during the instrument in-orbit test. The calibrated GEMS data is expected to be released by the end of 2020.

scholarly journals Spectral Calibration Algorithm for the Geostationary Environment Monitoring Spectrometer (GEMS)

2020 ◽  
Author(s):  
Mina Kang ◽  
Myoung-Hwan Ahn ◽  
Xiong Liu ◽  
Ukkyo Jeong ◽  
Jhoon Kim
Keyword(s):  
High Resolution ◽  
Signal To Noise Ratio ◽  
Spectral Response ◽  
Nonlinear Least Squares ◽  
Reference Spectrum ◽  
Environment Monitoring ◽  
Spectral Parameters ◽  
Spectral Calibration ◽  
Sensitivity Tests ◽  
Calibration Algorithm

The Geostationary Environment Monitoring Spectrometer (GEMS) onboard the Geostationary Korean Multi-Purpose Satellite 2B was successfully launched in February 2020. GEMS is a hyperspectral spectrometer measuring solar irradiance and Earth radiance in the range of 300 to 500 nm. This paper introduces the spectral calibration algorithm for GEMS, which uses a nonlinear least-squares approach. To assess the performance of the algorithm, sensitivity tests for a series of spectral parameters such as shift, spectral range for fitting, signal-to-noise ratio, spectral response function (SRF), and reference spectrum have been conducted. To improve the assessment, a synthetic GEMS spectrum using the prelaunch GEMS SRF is adopted here. The test results show that the required accuracy (0.002 nm) is achievable for the expected uncertainties of the parameters except for the SRF and the choice of high-resolution reference spectrum, which degrade the algorithm performance by an order magnitude. To mitigate the sensitivity to SRF, retrieval of in-orbit SRF using an analytic function is suggested. Finally, a few candidates for the high-resolution solar reference spectrum are prepared for testing by the instrument during in-orbit tests.

Characterization of the in-flight spectral response function of Geostationary Environment Monitoring Spectrometer (GEMS) retrieved using observed solar irradiance

2021 ◽  
Author(s):  
Mina Kang ◽  
Myoung-Hwan Ahn ◽  
Dai Ho Ko ◽  
Jhoon Kim ◽  
Dennis Nicks ◽  
...  
Keyword(s):  
Spectral Response ◽  
Trace Gases ◽  
Reference Spectrum ◽  
Environment Monitoring ◽  
Spatiotemporal Resolution ◽  
Hybrid Form ◽  
Spatial Direction ◽  
Spectral Fitting ◽  
Successful Launch

<p>The successful launch of Geostationary Environment Monitoring Spectrometer (GEMS) onboard the Geostationary Korea Multipurpose Satellite 2B (GK-2B) opens up a new possibility to provide daily air quality information for trace gases and aerosols over East Asia with high spatiotemporal resolution. As a part of major efforts to calibrate and validate the performance of the GEMS, accurate characterization of the spectral response functions (SRFs) is critical. The characteristics of preflight SRFs examined in terms of shape, width, skewness, and kurtosis vary smoothly along both the spectral and spatial direction thanks to highly symmetrical optic system of GEMS. While the preflight SRFs are determined with high accuracy, there is possibility of changes of in-flight SRFs during the harsh launch processes and/or operations over the mission lifetime. Thus, it is important to verify the in-flight SRFs after launch and to continue monitoring of their variability over time to assure the reliable trace gases retrievals. Here, we retrieve the in-flight SRFs for all spectral and spatial domain of the GEMS using spectral fitting of observed daily solar measurement and high-resolution solar reference spectrum. A variety of analytic model functions including hybrid form of Gaussian and flat-topped function, asymmetric super Gaussian, Voigt function are tested to determine the best representative function for GEMS SRF. The SRFs retrieved from early solar irradiances measured during the in-orbit tests agree well with the preflight SRFs indicating that no significant change occurred during the launch process. Continuous monitoring of the in-flight SRF is planned, using daily solar irradiances to investigate the temporal variation along with spectral and spatial directions. The detailed results of the in-flight SRF retrieval are to be presented.</p>

scholarly journals Spectral Calibration Requirements of Radio Interferometers for Epoch of Reionisation Science with the SKA

2016 ◽  
Vol 33 ◽  
Author(s):  
Cathryn M. Trott ◽  
Randall B. Wayth
Keyword(s):  
Thermal Noise ◽  
Spectral Response ◽  
Order Term ◽  
Spectral Characteristics ◽  
Primary Beam ◽  
Noise Power ◽  
Science Data ◽  
Spectral Calibration ◽  
Fourth Order Term ◽  
Complete Frequency

AbstractSpectral features introduced by instrumental chromaticity of radio interferometers have the potential to negatively impact the ability to perform Epoch of Reionisation and Cosmic Dawn (EoR/CD) science. We describe instrument calibration choices that influence the spectral characteristics of the science data, and assess their impact on EoR/CD statistical and tomographic experiments. Principally, we consider the intrinsic spectral response of the antennas, embedded within a complete frequency-dependent primary beam response, and instrument sampling. The analysis is applied to the proposed SKA1-Low EoR/CD experiments. We provide tolerances on the smoothness of the SKA station primary beam bandpass, to meet the scientific goals of statistical and tomographic (imaging) of EoR/CD programs. Two calibration strategies are tested: (1) fitting of each fine channel independently, and (2) fitting of annth-order polynomial for each ~ 1 MHz coarse channel with (n+1)th-order residuals (n= 2, 3, 4). Strategy (1) leads to uncorrelated power in the 2D power spectrum proportional to the thermal noise power, thereby reducing the overall sensitivity. Strategy (2) leads to correlated residuals from the fitting, and residual signal power with (n+1)th-order curvature. For the residual power to be less than the thermal noise, the fractional amplitude of a fourth-order term in the bandpass across a single coarse channel must be < 2.5% (50 MHz), < 0.5% (150 MHz), < 0.8% (200 MHz). The tomographic experiment places constraints on phase residuals in the bandpass. We find that the root-mean-square variability over all stations of the change in phase across any fine channel (4.578 kHz) should not exceed 0.2 degrees.

Design of the Remote Environment Monitoring System Based on Virtual Instrument

2012 ◽  
Vol 155-156 ◽  
pp. 111-114 ◽  
Author(s):  
Rong Chun Sun ◽  
Xue Son
Keyword(s):  
Instrument Development ◽  
Virtual Instrument ◽  
Test Results ◽  
Environment Monitoring ◽  
Development Platform ◽  
High Intelligence ◽  
Data Acquisition Card ◽  
Remote Environment ◽  
Measurement Devices ◽  
Remote Client

Environment monitoring technology is widely applied in industry, agriculture and other fields. Engineers usually need to integrate multiple measurement devices to complete a monitoring tusk, and make these different devices to be connected, which always spend a lot of time. Based on virtual instrument development platform, this paper described how to achieve the temperature and humidity data collection via the data acquisition card, sensors and PC, and realized the real-time display on the remote client through the DataSocket technology. The test results show that the system has the advantages of convenient operation, high intelligence and high accuracy, compared with the traditional instruments.

scholarly journals Technical note: A low-cost albedometer for snow and ice measurements &#8211; Theoretical results and application on a tropical mountain in Bolivia

2018 ◽  
Author(s):  
Thomas Condom ◽  
Marie Dumont ◽  
Lise Mourre ◽  
Jean Emmanuel Sicart ◽  
Antoine Rabatel ◽  
...  
Keyword(s):  
Solar Irradiance ◽  
Low Cost ◽  
Spectral Response ◽  
Lateral Moraine ◽  
Clear Sky ◽  
Direct Observations ◽  
Right Hand ◽  
The Right ◽  
Theoretical Results ◽  
Daily Time

Abstract. This study presents a new instrument called a low-cost albedometer (LCA) composed of two illuminance sensors that are used to measure in-situ incident and reflected illuminance values on a daily timescale. The ratio between reflected vs. incident illuminances is called the albedo index and can be compared with actual albedo values. Due to the shape of the sensor, the direct radiation for zenith angles ranging from 55° to 90° is not measured. The spectral response of the LCA varies with the solar irradiance wavelengths within the range 0.26 to 1.195 µm, and the LCA detects 85 % of the total spectral solar irradiance for clear sky conditions. We first consider the theoretical results obtained for 10 different ice and snow surfaces with clear sky and cloudy sky incident solar irradiance that show that the LCA spectral response may be responsible for an overestimation of the theoretical albedo values by roughly 9 % at most. Then, the LCA values are compared with two classical albedometers over a one-year measurement period (2013) for two sites in a tropical mountainous catchment in Bolivia. One site is located on the Zongo Glacier (i.e. snow and ice surfaces) and the second one is found on the right-hand side lateral moraine (bare soil and snow surfaces). The results, at daily time steps (256 days), given by the LCA are in good agreement with the classic albedo measurements taken with pyranometers with R2 = 0.83 (RMSD = 0.10) and R2 = 0.92 (RMSD = 0.08) for the Zongo Glacier and the right-hand side lateral moraine, respectively. This demonstrates that our system performs well and thus provides relevant opportunities to document spatio-temporal changes in the surface albedo from direct observations at the scale of an entire catchment at a low cost. Finally, during the period from September 2015 to June 2016, direct observations were collected with 15 LCAs on the Zongo Glacier and successfully compared with LANDSAT images showing the surface state of the glacier (i.e. snow or ice). This comparison illustrates the efficiency of this system to monitor the daily time step changes in the snow/ice coverage distributed on the glacier.

scholarly journals Spectral mismatch and its effect on artificial solar light source under standard test conditions

2021 ◽  
Vol 292 ◽  
pp. 01021
Author(s):  
Gao Sheng ◽  
Lu Xiaodong ◽  
Lun Shuxian
Keyword(s):  
Amorphous Silicon ◽  
Spectral Response ◽  
Solar Spectrum ◽  
Standard Test ◽  
Spectral Irradiance ◽  
Solar Light ◽  
Light Sources ◽  
Test Results ◽  
Test Conditions ◽  
The Difference

Under standard test conditions, the spectral irradiance of artificial solar light sources and the spectral response of photovoltaic devices are important factors that affect the accuracy of device test results. This paper takes the standard solar spectrum AM1.5 as a reference, and calculates the difference between the four commonly used artificial solar light sources (Arc Lamp, Q-Flash, Q-Flash w and ELH) and the standard solar spectrum AM1.5 from the perspective of spectral mismatch. The spectral mismatch factor and the output parameters of the amorphous silicon cell under the irradiation of these light sources. Calculations show that the spectral mismatch factor of Arc Lamp is only 1.005, which matches the standard solar spectrum AM1.5 best. Due to the effect of spectral mismatch, the output parameters of amorphous silicon cells will change significantly after different artificial light sources irradiate them.

scholarly journals Preflight Spectral Calibration of Airborne Shortwave Infrared Hyperspectral Imager with Water Vapor Absorption Characteristics

Sensors ◽  
2019 ◽  
Vol 19 (10) ◽  
pp. 2259 ◽  
Author(s):  
Honglin Liu ◽  
Dong Zhang ◽  
Yueming Wang
Keyword(s):  
Water Vapor ◽  
Spectral Response ◽  
Spectral Characteristics ◽  
Calibration Method ◽  
Least Square ◽  
Response Functions ◽  
Water Vapor Absorption ◽  
Gaussian Shape ◽  
Spectral Calibration ◽  
Calibration Uncertainty

Due to the strong absorption of water vapor at wavelengths of 1350–1420 nm and 1820–1940 nm, under normal atmospheric conditions, the actual digital number (DN) response curve of a hyperspectral imager deviates from the Gaussian shape, which leads to a decrease in the calibration accuracy of an instrument’s spectral response functions (SRF). The higher the calibration uncertainty of SRF, the worse the retrieval accuracy of the spectral characteristics of the targets. In this paper, an improved spectral calibration method based on a monochromator and the spectral absorptive characteristics of water vapor in the laboratory is presented. The water vapor spectral calibration method (WVSCM) uses the difference function to calculate the intrinsic DN response functions of the spectral channels located in the absorptive wavelength range of water vapor and corrects the wavelength offset of the monochromator via the least-square procedure to achieve spectral calibration throughout the full spectral responsive range of the hyper-spectrometer. The absolute spectral calibration uncertainty is ±0.125 nm. We validated the effectiveness of the WVSCM with two tunable semiconductor lasers, and the spectral wavelength positions calibrated by lasers and the WVSCM showed a good degree of consistency.

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