scholarly journals Spectral calibration of the MethaneAIR instrument

2021 ◽  
Vol 14 (5) ◽  
pp. 3737-3753
Author(s):  
Carly Staebell ◽  
Kang Sun ◽  
Jenna Samra ◽  
Jonathan Franklin ◽  
Christopher Chan Miller ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Spectral Response ◽  
Point Sources ◽  
Stray Light ◽  
Lookup Table ◽  
High Spectral Resolution ◽  
Retrieval Algorithm ◽  
Co2 Absorption ◽  
Central Wavelength ◽  
Spectral Calibration

Abstract. MethaneAIR is the airborne simulator of MethaneSAT, an area-mapping satellite currently under development with the goal of locating and quantifying large anthropogenic CH4 point sources as well as diffuse emissions at the spatial scale of an oil and gas basin. Built to closely replicate the forthcoming satellite, MethaneAIR consists of two imaging spectrometers. One detects CH4 and CO2 absorption around 1.65 and 1.61 µm, respectively, while the other constrains the optical path in the atmosphere by detecting O2 absorption near 1.27 µm. The high spectral resolution and stringent retrieval accuracy requirements of greenhouse gas remote sensing in this spectral range necessitate a reliable spectral calibration. To this end, on-ground laboratory measurements were used to derive the spectral calibration of MethaneAIR, serving as a pathfinder for the future calibration of MethaneSAT. Stray light was characterized and corrected for through fast-Fourier-transform-based Van Cittert deconvolution. Wavelength registration was examined and found to be best described by a linear relationship for both bands with a precision of ∼ 0.02 spectral pixel. The instrument spectral spread function (ISSF), measured with fine wavelength steps of 0.005 nm near a series of central wavelengths across each band, was oversampled to construct the instrument spectral response function (ISRF) at each central wavelength and spatial pixel. The ISRFs were smoothed with a Savitzky–Golay filter for use in a lookup table in the retrieval algorithm. The MethaneAIR spectral calibration was evaluated through application to radiance spectra from an instrument flight over the Colorado Front Range.

scholarly journals Spectral Calibration of the MethaneAIR Instrument

2021 ◽  
Author(s):  
Carly Staebell ◽  
Kang Sun ◽  
Jenna Samra ◽  
Jonathan Franklin ◽  
Christopher Chan Miller ◽  
...  
Keyword(s):  
Spectral Response ◽  
Stray Light ◽  
Lookup Table ◽  
Colorado Front Range ◽  
High Spectral Resolution ◽  
Retrieval Algorithm ◽  
Co2 Absorption ◽  
Central Wavelength ◽  
Spectral Calibration ◽  
Basin Scale

Abstract. MethaneAIR is the airborne simulator of MethaneSAT, an area-mapping satellite currently under development with the goal of locating and quantifying large anthropogenic point CH4 sources as well as diffuse basin-scale emissions. Built to closely replicate the forthcoming satellite, MethaneAIR consists of two imaging spectrometers. One detects CH4 and CO2 absorption around 1.65 and 1.61 μm, respectively, while the other constrains the optical path in the atmosphere by detecting O2 absorption near 1.27 μm. The high spectral resolution and stringent retrieval accuracy requirements of greenhouse gas remote sensing in this spectral range necessitate a reliable spectral calibration. To this end, on-ground laboratory measurements were used to derive the spectral calibration of MethaneAIR, serving as a pathfinder for the future calibration of MethaneSAT. Stray light was characterized and corrected through Fast Fourier Transform (FFT)-based Van Cittert deconvolution. Wavelength registration was examined and found to be best described by a linear relationship for both bands with a precision of ~0.02 spectral pixel. The instrument spectral spread function (ISSF), measured with fine wavelength steps of 0.005 nm near a series of central wavelengths across each band, was oversampled to construct the instrument spectral response function (ISRF) at each central wavelength and spatial pixel. The ISRFs were smoothed with a Savitzky-Golay filter for use in a lookup table in the retrieval algorithm. The MethaneAIR spectral calibration was evaluated through application to radiance spectra from an instrument flight over the Colorado Front Range.

scholarly journals Bias assessment of lower and middle tropospheric CO<sub>2</sub> concentrations of GOSAT/TANSO-FTS TIR Version 1 product

2017 ◽  
Author(s):  
Naoko Saitoh ◽  
Shuhei Kimoto ◽  
Ryo Sugimura ◽  
Ryoichi Imasu ◽  
Kei Shiomi ◽  
...  
Keyword(s):  
Bias Correction ◽  
Lower Troposphere ◽  
Point Sources ◽  
Upper Atmosphere ◽  
Retrieval Algorithm ◽  
Co2 Absorption ◽  
Free Troposphere ◽  
Absorption Bands ◽  
Co2 Concentrations ◽  
Local Point

Abstract. CO2 observations in the free troposphere can be useful for constraining CO2 source and sink estimates at the surface due to their representativeness being away from local point sources of CO2. The thermal infrared (TIR) band of the Thermal and Near Infrared Sensor for Carbon Observation (TANSO)−Fourier Transform Spectrometer (FTS) on board the Greenhouse Gases Observing Satellite (GOSAT) has been observing global CO2 concentrations in the free troposphere for about 8 years, and thus could provide a dataset with which to evaluate the vertical transport of CO2 from the surface to the upper atmosphere. This study evaluated biases in the TIR version 1 (V1) CO2 product in the lower troposphere (LT) and the middle troposphere (MT) (736–287 hPa), on the basis of comparisons with CO2 profiles obtained over airports using Continuous CO2 Measuring Equipment (CME) in the Comprehensive Observation Network for Trace gases by AIrLiner (CONTRAIL) project. Bias-correction values are presented for TIR CO2 data for each pressure layer in the LT and MT regions during each season and in each latitude band: 40°S–20°S, 20° S–20° N, 20° N–40° N, and 40° N–60° N. TIR V1 CO2 data had consistent negative biases of 1–1.5 % compared with CME CO2 data in the LT and MT regions, with the largest negative biases at 541–398 hPa, partly due to the use of 10-μm CO2 absorption band in conjunction with 15-μm and 9-μm absorption bands in the V1 retrieval algorithm. Global comparisons between TIR CO2 data to which the bias-correction values were applied and CO2 data simulated by Nonhydrostatic ICosahedral Atmospheric Model (NICAM)-based transport model (TM) confirmed the validity of the bias-correction values evaluated over airports in limited areas. In low latitudes in the upper MT region (398–287 hPa), however, TIR CO2 data in northern summer were overcorrected by these bias-correction values; this is because the bias-correction values were determined using comparisons mainly over airports in East Asia where CO2 concentrations in the upper atmosphere display relatively large variations due to strong updrafts.

scholarly journals Retrieval Algorithm for the Column CO<sub>2</sub> Mixing Ratio from Pulsed Multi-Wavelength Lidar Measurements

2020 ◽  
Author(s):  
Xiaoli Sun ◽  
James B. Abshire ◽  
Anand Ramanathan ◽  
S. Randy Kawa ◽  
Jianping Mao
Keyword(s):  
Least Squares ◽  
Absorption Line ◽  
Linear Trend ◽  
Spectral Response ◽  
Retrieval Algorithm ◽  
Co2 Absorption ◽  
Mixing Ratio ◽  
Atmospheric Transmission ◽  
Least Squares Fit ◽  
Multi Wavelength

Abstract. The retrieval algorithm for the column mixing ratio of CO2 from the measurements of a pulsed multi-wavelength integrated path differential absorption (IPDA) lidar is described. The lidar samples the shape of the 1572.33 nm CO2 absorption line at 15 or 30 wavelengths. The algorithm uses a least-squares fit between the CO2 line shape computed from a layered atmosphere model to that sampled by the lidar. In addition to the column average CO2 dry air mole fraction (XCO2), several other parameters are also solved simultaneously from the fit. These include the Doppler shift in the received laser signal wavelengths, the product of the surface reflectivity and atmospheric transmission and a linear trend in the lidar receiver's spectral response. The algorithm can also be used to solve for the average water vapor mixing ratio, which causes a secondary absorption in the wings of the CO2 absorption line under high humidity conditions. The least-squares fit is linearized about the expected XCO2 value which allows the use of a standard linear least-squares fitting method and software tools. The standard deviation of the retrieved XCO2 is obtained from covariance matrix of the fit. An averaging kernel is defined similarly to that used for passive trace-gas sounding. Examples are presented of using the algorithm to retrieve XCO2 from the measurements from NASA Goddard's airborne CO2 Sounder lidar made at a constant altitude and during spiral-down maneuvers.

scholarly journals Retrieval algorithm for the column CO<sub>2</sub> mixing ratio from pulsed multi-wavelength lidar measurements

2021 ◽  
Vol 14 (5) ◽  
pp. 3909-3922
Author(s):  
Xiaoli Sun ◽  
James B. Abshire ◽  
Anand Ramanathan ◽  
Stephan R. Kawa ◽  
Jianping Mao
Keyword(s):  
Least Squares ◽  
Absorption Line ◽  
Linear Trend ◽  
Spectral Response ◽  
Retrieval Algorithm ◽  
Co2 Absorption ◽  
Mixing Ratio ◽  
Atmospheric Transmission ◽  
Least Squares Fit ◽  
Multi Wavelength

Abstract. The retrieval algorithm for CO2 column mixing ratio from measurements of a pulsed multi-wavelength integrated path differential absorption (IPDA) lidar is described. The lidar samples the shape of the 1572.33 nm CO2 absorption line at multiple wavelengths. The algorithm uses a least-squares fit between the CO2 line shape computed from a layered atmosphere model and that sampled by the lidar. In addition to the column-average CO2 dry-air mole fraction (XCO2), several other parameters are also solved simultaneously from the fit. These include the Doppler shift at the received laser signal wavelength, the product of the surface reflectivity and atmospheric transmission, and a linear trend in the lidar receiver's spectral response. The algorithm can also be used to solve for the average water vapor mixing ratio, which produces a secondary absorption in the wings of the CO2 absorption line under humid conditions. The least-squares fit is linearized about the expected XCO2 value, which allows the use of a standard linear least-squares fitting method and software tools. The standard deviation of the retrieved XCO2 is obtained from the covariance matrix of the fit. The averaging kernel is also provided similarly to that used for passive trace-gas column measurements. Examples are presented of using the algorithm to retrieve XCO2 from measurements of the NASA Goddard airborne CO2 Sounder lidar that were made at constant altitude and during spiral-down profile maneuvers.

Characterization of GEMS level 1B based on inter-comparison using the visible channel of AMI

2021 ◽  
Author(s):  
Yeeun Lee ◽  
Myoung-Hwan Ahn ◽  
Mijin Eo ◽  
Mina Kang ◽  
Kyung-jung Moon ◽  
...  
Keyword(s):  
Optical System ◽  
Solar Irradiance ◽  
Spectral Response ◽  
Atmospheric Composition ◽  
Asia Pacific ◽  
High Spectral Resolution ◽  
Data Set ◽  
Central Wavelength ◽  
The North ◽  
The Earth

&lt;p&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; The Geostationary Korean Multi-Purpose Satellite (GK-2) program consisting of GK-2A and GK-2B provides consistent monitoring information in the Asia Pacific region, including the Korean peninsula. The Geostationary Environment Monitoring Spectrometer (GEMS) onboard GK-2B in particular provides information on the atmospheric composition and aerosol properties, retrieved from the calibrated radiance (Level 1B) with high spectral resolution in 300-500 nm. GEMS started its extended validation measurement after the in-orbit test (IOT) in October following the launch of the satellite in February 2020. One of issues found during the IOT is that GEMS shows a spatial dependence in the measured solar irradiance along the north-south direction, albeit the solar irradiance does not have such a dependency. Thus, such a dependence should be from the optical system or the solar diffuser which is placed in front of the scan mirror. To clarify the root cause of the dependence, we utilize inter-comparison of the Earth measurement between GEMS and the Advanced Meteorological Imager (AMI), a multi-channel imager onboard GK-2A for meteorological monitoring. As the spectral range of GEMS fully covers the spectral response function (SRF) of the AMI visible channel having a central wavelength of 470 nm, spectral matching is properly done by convolving the SRF with the hyperspectral data of GEMS. By taking advantage of the fact that the position of GK-2A and GK-2B is maintained within a 0.5 degree square box centered at 128.2&amp;#176;E, match-up data set for the inter-comparison is prepared by temporal and spatial collocation. To reduce spatio-temporal mis-match and increase the signal to noise, zonal mean is applied to the collocated data. Results show that the north-south dependence occurs in the comparison of reflectance, the ratio between the earth radiance and solar irradiance, while not in the comparison of radiance. This indicates the dependence occurs due to the characteristics of the solar diffuser, not because of optical system. It is further deduced that dependence of diffuser transmittance on the solar azimuth angle is the main cause of the north-south dependency which was not characterized during the pre-flight ground test.&lt;/p&gt;

scholarly journals Hyperspectral Data Simulation (Sentinel-2 to AVIRIS-NG) for Improved Wildfire Fuel Mapping, Boreal Alaska

2021 ◽  
Vol 13 (9) ◽  
pp. 1693
Author(s):  
Anushree Badola ◽  
Santosh K. Panda ◽  
Dar A. Roberts ◽  
Christine F. Waigl ◽  
Uma S. Bhatt ◽  
...  
Keyword(s):  
Land Cover ◽  
Spectral Resolution ◽  
Hyperspectral Image ◽  
Spectral Response ◽  
Spectral Characteristics ◽  
Hyperspectral Data ◽  
Spectral Unmixing ◽  
High Spectral Resolution ◽  
Fuel Mapping ◽  
Sentinel 2

Alaska has witnessed a significant increase in wildfire events in recent decades that have been linked to drier and warmer summers. Forest fuel maps play a vital role in wildfire management and risk assessment. Freely available multispectral datasets are widely used for land use and land cover mapping, but they have limited utility for fuel mapping due to their coarse spectral resolution. Hyperspectral datasets have a high spectral resolution, ideal for detailed fuel mapping, but they are limited and expensive to acquire. This study simulates hyperspectral data from Sentinel-2 multispectral data using the spectral response function of the Airborne Visible/Infrared Imaging Spectrometer-Next Generation (AVIRIS-NG) sensor, and normalized ground spectra of gravel, birch, and spruce. We used the Uniform Pattern Decomposition Method (UPDM) for spectral unmixing, which is a sensor-independent method, where each pixel is expressed as the linear sum of standard reference spectra. The simulated hyperspectral data have spectral characteristics of AVIRIS-NG and the reflectance properties of Sentinel-2 data. We validated the simulated spectra by visually and statistically comparing it with real AVIRIS-NG data. We observed a high correlation between the spectra of tree classes collected from AVIRIS-NG and simulated hyperspectral data. Upon performing species level classification, we achieved a classification accuracy of 89% for the simulated hyperspectral data, which is better than the accuracy of Sentinel-2 data (77.8%). We generated a fuel map from the simulated hyperspectral image using the Random Forest classifier. Our study demonstrated that low-cost and high-quality hyperspectral data can be generated from Sentinel-2 data using UPDM for improved land cover and vegetation mapping in the boreal forest.

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.

Spectral calibration of Fengyun-3 satellite high-spectral resolution infrared sounder

2019 ◽  
Vol 27 (4) ◽  
pp. 747-755 ◽  
Author(s):  
漆成莉 QI Cheng-li ◽  
周 方 ZHOU Fang ◽  
吴春强 WU Chun-qiang ◽  
胡秀清 HU Xiu-qing ◽  
顾明剑 GU Ming-jian
Keyword(s):  
Spectral Resolution ◽  
High Spectral Resolution ◽  
Spectral Calibration

scholarly journals A Spectra Classification Methodology of Hyperspectral Infrared Images for Near Real-Time Estimation of the SO2 Emission Flux from Mount Etna with LARA Radiative Transfer Retrieval Model

2020 ◽  
Vol 12 (24) ◽  
pp. 4107
Author(s):  
Charlotte Segonne ◽  
Nathalie Huret ◽  
Sébastien Payan ◽  
Mathieu Gouhier ◽  
Valéry Catoire
Keyword(s):  
Radiative Transfer ◽  
Real Time ◽  
Mount Etna ◽  
High Spectral Resolution ◽  
Retrieval Algorithm ◽  
Volcanic Plume ◽  
Transfer Model ◽  
So2 Emission ◽  
North East ◽  
Emission Fluxes

Fast and accurate quantification of gas fluxes emitted by volcanoes is essential for the risk mitigation of explosive eruption, and for the fundamental understanding of shallow eruptive processes. Sulphur dioxide (SO2), in particular, is a reliable indicator to predict upcoming eruptions, and its systemic characterization allows the rapid assessment of sudden changes in eruptive dynamics. In this regard, infrared (IR) hyperspectral imaging is a promising new technology for accurately measure SO2 fluxes day and night at a frame rate down to 1 image per second. The thermal infrared region is not very sensitive to particle scattering, which is an asset for the study of volcanic plume. A ground based infrared hyperspectral imager was deployed during the IMAGETNA campaign in 2015 and provided high spectral resolution images of the Mount Etna (Sicily, Italy) plume from the North East Crater (NEC), mainly. The LongWave InfraRed (LWIR) hyperspectral imager, hereafter name Hyper-Cam, ranges between 850–1300 cm−1 (7.7–11.8 µm). The LATMOS (Laboratoire Atmosphères Milieux Observations Spatiales) Atmospheric Retrieval Algorithm (LARA), which is used to retrieve the slant column densities (SCD) of SO2, is a robust and a complete radiative transfer model, well adapted to the inversion of ground-based remote measurements. However, the calculation time to process the raw data and retrieve the infrared spectra, which is about seven days for the retrieval of one image of SO2 SCD, remains too high to infer near real-time (NRT) SO2 emission fluxes. A spectral image classification methodology based on two parameters extracting spectral features in the O3 and SO2 emission bands was developed to create a library. The relevance is evaluated in detail through tests. From data acquisition to the generation of SO2 SCD images, this method requires only ~40 s per image, which opens the possibility to infer NRT estimation of SO2 emission fluxes from IR hyperspectral imager measurements.

scholarly journals A Sensitivity Study of the 4.8 µm Carbon Dioxide Absorption Band in the MWIR Spectral Range

2020 ◽  
Vol 12 (1) ◽  
pp. 172 ◽  
Author(s):  
Vito Romaniello ◽  
Claudia Spinetti ◽  
Malvina Silvestri ◽  
Maria Fabrizia Buongiorno
Keyword(s):  
Carbon Dioxide ◽  
Absorption Band ◽  
Strong Dependence ◽  
Point Sources ◽  
Channel Width ◽  
Anthropogenic Sources ◽  
Co2 Absorption ◽  
Industrial Emissions ◽  
Surface Temperatures ◽  
Concentration Changes

The measurements of gas concentrations in the atmosphere are recently developed thanks to the availability of gases absorbing spectral channels in space sensors and strictly depending on the instrument performances. In particular, measuring the sources of carbon dioxide is of high interest to know the distribution, both spatial and vertical, of this greenhouse gas and quantify the natural/anthropogenic sources. The present study aims to understand the sensitivity of the CO2 absorption band at 4.8 µm to possibly detect and measure the spatial distribution of emissions from point sources (i.e., degassing volcanic plumes, fires, and industrial emissions). With the aim to define the characteristics of future multispectral imaging space radiometers, the performance of the CO2 4.8 µm absorption band was investigated. Simulations of the “Top of Atmosphere” (TOA) radiance have been performed by using real input data to reproduce realistic scenarios on a volcanic high elevation point source (>2 km): actual atmospheric background of CO2 (~400 ppm) and vertical atmospheric profiles of pressure, temperature, and humidity obtained from probe balloons. The sensitivity of the channel to the CO2 concentration has been analyzed also varying surface temperatures as environmental conditions from standard to high temperature. Furthermore, response functions of operational imaging sensors in the middle wave infrared spectral region were used. The channel width values of 0.15 µm and 0.30 µm were tested in order to find changes in the gas concentration. Simulations provide results about the sensitivity necessary to appreciate carbon dioxide concentration changes considering a target variation of 10 ppm in gas column concentration. Moreover, the results show the strong dependence of at-sensor radiance on the surface temperature: radiances sharply increase, from 1 Wm−2sr−1µm−1 (in the “standard condition”) to >1200 Wm−2sr−1µm−1 (in the warmest case) when temperatures increase from 300 to 1000 K. The highest sensitivity has been obtained considering the channel width equal to 0.15 µm with noise equivalent delta temperature (NEDT) values in the range from 0.045 to 0.56 K at surface temperatures ranging from 300 to 1000 K.

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