Most existing endmember extraction techniques require prior knowledge about the number of endmembers in a hyperspectral image. The number of endmembers is normally estimated by a separate procedure, whose accuracy has a large influence on the endmember extraction performance. In order to bridge the two seemingly independent but, in fact, highly correlated procedures, we develop a new endmember estimation strategy that simultaneously counts and extracts endmembers. We consider a hyperspectral image as a hyperspectral pixel set and define the subset of pixels that are most different from one another as the divergent subset (DS) of the hyperspectral pixel set. The DS is characterized by the condition that any additional pixel would increase the likeness within the DS and, thus, reduce its divergent degree. We use the DS as the endmember set, with the number of endmembers being the subset cardinality. To render a practical computation scheme for identifying the DS, we reformulate it in terms of a quadratic optimization problem with a numerical solution. In addition to operating as an endmember estimation algorithm by itself, the DS method can also co-operate with existing endmember extraction techniques by transforming them into a novel and more effective schemes. Experimental results validate the effectiveness of the DS methodology in simultaneously counting and extracting endmembers not only as an individual algorithm but also as a foundation algorithm for improving existing methods. Our full code is released for public evaluation.11
https://github.com/xuanwentao/DivergentSubset
The Landsat 1-5 multispectral scanner system (MSS) collected records of land surface mainly during 1972-1992. Investigations on MSS have been relatively limited compared with the numerous investigations on its successors, such as Thematic Mapper (TM) and Enhanced TM Plus (ETM+). The benefits of the Landsat program are not fully accomplished without the inclusion of MSS archives. Investigations on the Landsat 1-5 MSS channel reflectance characteristics wereperformed followed by derived vegetation spectral indices and the Tasseled Cap (TC) transformed features mainly using a collection of synthesized records. On average, the Landsat 4 MSS is generally comparable to the Landsat 5 MSS. The Landsat 1-3 MSSs show disagreement in channel reflectance compared with the Landsat 5 MSS, especially for the red channel (600-700 nm) and the near-infrared channel (700-800 nm). Meanwhile, the relative differences for vegetation spectral indices of the Landsat 3 MSS are mainly from -16% to -5% with the median about -11.5%, while those of the Landsat 2 MSS are mainly from -15% to -7%. Cross-validation tests and two case applications suggested that between-sensor consistency was improved generally through the transformation models generated by ordinary least-squares regression. To improve the consistency of the vegetation indices and the TC greenness, direct strategy employing respective transformation models was more effective than calculations based on the transformed channel reflectance. Considering the shortages of the Landsat MSS archives, further efforts are needed to improve its comparability with observations by other successive Landsat sensors.
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Correcting the impact of the isotope composition on the mixing ratio dependency of water vapour isotope measurements with cavity ring-down spectrometers
Yongbiao Weng, Alexandra Touzeau, and Harald Sodemann
Atmos. Meas. Tech., 13, 3167–3190, https://doi.org/10.5194/amt-13-3167-2020, 2020
We find that the known mixing ratio dependence of laser spectrometers for water vapour isotope measurements varies with isotope composition. We have developed a scheme to correct for this isotope-composition-dependent bias. The correction is most substantial at low mixing ratios. Stability tests indicate that the first-order dependency is a constant instrument characteristic. Water vapour isotope measurements at low mixing ratios can now be corrected by following our proposed procedure.
Correcting the impact of the isotope composition on the mixing ratio dependency of water vapour isotope measurements with cavity ring-down spectrometers
Yongbiao Weng, Alexandra Touzeau, and Harald Sodemann
Atmos. Meas. Tech., 13, 3167–3190, https://doi.org/10.5194/amt-13-3167-2020, 2020
We find that the known mixing ratio dependence of laser spectrometers for water vapour isotope measurements varies with isotope composition. We have developed a scheme to correct for this isotope-composition-dependent bias. The correction is most substantial at low mixing ratios. Stability tests indicate that the first-order dependency is a constant instrument characteristic. Water vapour isotope measurements at low mixing ratios can now be corrected by following our proposed procedure.
An extended radar relative calibration adjustment (eRCA) technique for higher-frequency radars and range–height indicator (RHI) scans
Alexis Hunzinger, Joseph C. Hardin, Nitin Bharadwaj, Adam Varble, and Alyssa Matthews
Atmos. Meas. Tech., 13, 3147–3166, https://doi.org/10.5194/amt-13-3147-2020, 2020
The calibration of weather radars is one of the most dominant sources of errors hindering their use. This work takes a technique for tracking the changes in radar calibration using the radar clutter from the ground and extends it to higher-frequency research radars. It demonstrates that after modifications the technique is successful but that special care needs to be taken in its application at high frequencies. The technique is verified using data from multiple DOE ARM field campaigns.
Validation of TROPOMI Surface UV Radiation Product
Kaisa Lakkala, Jukka Kujanpää, Colette Brogniez, Nicolas Henriot, Antti Arola, Margit Aun, Frédérique Auriol, Alkiviadis F. Bais, Germar Bernhard, Veerle De Bock, Maxime Catalfamo, Christine Deroo, Henri Diémoz, Luca Egli, Jean-Baptiste Forestier, Ilias Fountoulakis, Rosa Delia Garcia, Julian Gröbner, Seppo Hassinen, Anu Heikkilä, Stuart Henderson, Gregor Hülsen, Bjørn Johnsen, Niilo Kalakoski, Angelos Karanikolas, Tomi Karppinen, Kevin Lamy, Sergio F. León-Luis, Anders V. Lindfors, Jean-Marc Metzger, Fanny Minvielle, Harel B. Muskatel, Thierry Portafaix, Alberto Redondas, Ricardo Sanchez, Anna Maria Siani, Tove Svendby, and Johanna Tamminen
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-121,2020
Preprint under review for AMT (discussion: open, 0 comments)
The TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor (S5P) satellite was launched on 13 October 2017 to provide the atmospheric composition for atmosphere and climate research. Ground-based data from 25 sites located in arctic, subarctic, temperate, equatorial and antarctic
areas were used for validation of the TROPOMI Surface Ultraviolet (UV) Radiation Product. For most sites 60–80 % of TROPOMI data was within ±20 % from ground-based data.
The Importance of Size Ranges in Aerosol Instrument Intercomparisons: A Case Study for the ATom Mission
Hongyu Guo, Pedro Campuzano-Jost, Benjamin A. Nault, Douglas A. Day, Jason C. Schroder, Jack E. Dibb, Maximilian Dollner, Bernadett Weinzierl, and Jose L. Jimenez
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-224,2020
Preprint under review for AMT (discussion: open, 0 comments)
We utilize a set of high-quality datasets collected during the NASA ATom aircraft mission to investigate the impact of differences in observable particle sizes across aerosol instruments, in aerosol measurement comparisons. Very good agreement was found between chemically and physically derived submicron aerosol volume. Results support a lack of significant unknown biases in the response of Aerodyne Aerosol Mass Spectrometer (AMS) when sampling remote aerosols across the globe.
An extended radar relative calibration adjustment (eRCA) technique for higher-frequency radars and range–height indicator (RHI) scans
Alexis Hunzinger, Joseph C. Hardin, Nitin Bharadwaj, Adam Varble, and Alyssa Matthews
Atmos. Meas. Tech., 13, 3147–3166, https://doi.org/10.5194/amt-13-3147-2020, 2020
The calibration of weather radars is one of the most dominant sources of errors hindering their use. This work takes a technique for tracking the changes in radar calibration using the radar clutter from the ground and extends it to higher-frequency research radars. It demonstrates that after modifications the technique is successful but that special care needs to be taken in its application at high frequencies. The technique is verified using data from multiple DOE ARM field campaigns.
Validation of TROPOMI Surface UV Radiation Product
Kaisa Lakkala, Jukka Kujanpää, Colette Brogniez, Nicolas Henriot, Antti Arola, Margit Aun, Frédérique Auriol, Alkiviadis F. Bais, Germar Bernhard, Veerle De Bock, Maxime Catalfamo, Christine Deroo, Henri Diémoz, Luca Egli, Jean-Baptiste Forestier, Ilias Fountoulakis, Rosa Delia Garcia, Julian Gröbner, Seppo Hassinen, Anu Heikkilä, Stuart Henderson, Gregor Hülsen, Bjørn Johnsen, Niilo Kalakoski, Angelos Karanikolas, Tomi Karppinen, Kevin Lamy, Sergio F. León-Luis, Anders V. Lindfors, Jean-Marc Metzger, Fanny Minvielle, Harel B. Muskatel, Thierry Portafaix, Alberto Redondas, Ricardo Sanchez, Anna Maria Siani, Tove Svendby, and Johanna Tamminen
Atmos. Meas. Tech. Discuss., https//doi.org/10.5194/amt-2020-121,2020
Preprint under review for AMT (discussion: open, 0 comments)
The TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor (S5P) satellite was launched on 13 October 2017 to provide the atmospheric composition for atmosphere and climate research. Ground-based data from 25 sites located in arctic, subarctic, temperate, equatorial and antarctic
areas were used for validation of the TROPOMI Surface Ultraviolet (UV) Radiation Product. For most sites 60–80 % of TROPOMI data was within ±20 % from ground-based data.
The Importance of Size Ranges in Aerosol Instrument Intercomparisons: A Case Study for the ATom Mission
Hongyu Guo, Pedro Campuzano-Jost, Benjamin A. Nault, Douglas A. Day, Jason C. Schroder, Jack E. Dibb, Maximilian Dollner, Bernadett Weinzierl, and Jose L. Jimenez
Atmos. Meas. Tech. Discuss., https//doi.org/10.5194/amt-2020-224,2020
Preprint under review for AMT (discussion: open, 0 comments)
We utilize a set of high-quality datasets collected during the NASA ATom aircraft mission to investigate the impact of differences in observable particle sizes across aerosol instruments, in aerosol measurement comparisons. Very good agreement was found between chemically and physically derived submicron aerosol volume. Results support a lack of significant unknown biases in the response of Aerodyne Aerosol Mass Spectrometer (AMS) when sampling remote aerosols across the globe.
The development of the Atmospheric Measurements by Ultra-Light Spectrometer (AMULSE) greenhouse gas profiling system and application for satellite retrieval validation
Lilian Joly, Olivier Coopmann, Vincent Guidard, Thomas Decarpenterie, Nicolas Dumelié, Julien Cousin, Jérémie Burgalat, Nicolas Chauvin, Grégory Albora, Rabih Maamary, Zineb Miftah El Khair, Diane Tzanos, Joël Barrié, Éric Moulin, Patrick Aressy, and Anne Belleudy
Atmos. Meas. Tech., 13, 3099–3118, https://doi.org/10.5194/amt-13-3099-2020, 2020
This article presents an instrument weighing less than 3 kg for accurate and rapid measurement of greenhouse gases between 0 and 30 km altitude using a meteorological balloon. This article shows the interest of these measurements for the validation of simulations of infrared satellite observations.
Implementation of a chemical background method for atmospheric OH measurements by laser-induced fluorescence: characterisation and observations from the UK and China
Robert Woodward-Massey, Eloise J. Slater, Jake Alen, Trevor Ingham, Danny R. Cryer, Leanne M. Stimpson, Chunxiang Ye, Paul W. Seakins, Lisa K. Whalley, and Dwayne E. Heard
Atmos. Meas. Tech., 13, 3119–3146, https://doi.org/10.5194/amt-13-3119-2020, 2020
The OH radical is known as nature’s detergent, removing most trace gases from the atmosphere. Hence, an accurate measurement of its concentration is very important. We present measurements of OH in several field locations using a laser-based fluorescence method equipped with an OH scavenger. By determining the background signal in two different ways, we show that the instrument does not suffer any significant interferences that could result in an overestimation of OH concentrations.
Robust statistical calibration and characterization of portable low-cost air quality monitoring sensors to quantify real-time O
The development of the Atmospheric Measurements by Ultra-Light Spectrometer (AMULSE) greenhouse gas profiling system and application for satellite retrieval validation
Lilian Joly, Olivier Coopmann, Vincent Guidard, Thomas Decarpenterie, Nicolas Dumelié, Julien Cousin, Jérémie Burgalat, Nicolas Chauvin, Grégory Albora, Rabih Maamary, Zineb Miftah El Khair, Diane Tzanos, Joël Barrié, Éric Moulin, Patrick Aressy, and Anne Belleudy
Atmos. Meas. Tech., 13, 3099–3118, https://doi.org/10.5194/amt-13-3099-2020, 2020
This article presents an instrument weighing less than 3 kg for accurate and rapid measurement of greenhouse gases between 0 and 30 km altitude using a meteorological balloon. This article shows the interest of these measurements for the validation of simulations of infrared satellite observations.
Implementation of a chemical background method for atmospheric OH measurements by laser-induced fluorescence: characterisation and observations from the UK and China
Robert Woodward-Massey, Eloise J. Slater, Jake Alen, Trevor Ingham, Danny R. Cryer, Leanne M. Stimpson, Chunxiang Ye, Paul W. Seakins, Lisa K. Whalley, and Dwayne E. Heard
Atmos. Meas. Tech., 13, 3119–3146, https://doi.org/10.5194/amt-13-3119-2020, 2020
The OH radical is known as nature’s detergent, removing most trace gases from the atmosphere. Hence, an accurate measurement of its concentration is very important. We present measurements of OH in several field locations using a laser-based fluorescence method equipped with an OH scavenger. By determining the background signal in two different ways, we show that the instrument does not suffer any significant interferences that could result in an overestimation of OH concentrations.
Robust statistical calibration and characterization of portable low-cost air quality monitoring sensors to quantify real-time O