{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,24]],"date-time":"2026-06-24T15:11:51Z","timestamp":1782313911028,"version":"3.54.5"},"reference-count":22,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2022,6,18]],"date-time":"2022-06-18T00:00:00Z","timestamp":1655510400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Talent fund of Hefei University","award":["22040421002"],"award-info":[{"award-number":["22040421002"]}]},{"name":"Talent fund of Hefei University","award":["KJ2021A0979"],"award-info":[{"award-number":["KJ2021A0979"]}]},{"name":"Talent fund of Hefei University","award":["2018xk03"],"award-info":[{"award-number":["2018xk03"]}]},{"name":"Talent fund of Hefei University","award":["ANR-10-LABX-005"],"award-info":[{"award-number":["ANR-10-LABX-005"]}]},{"name":"University Natural Science Research Program of Anhui Province","award":["22040421002"],"award-info":[{"award-number":["22040421002"]}]},{"name":"University Natural Science Research Program of Anhui Province","award":["KJ2021A0979"],"award-info":[{"award-number":["KJ2021A0979"]}]},{"name":"University Natural Science Research Program of Anhui Province","award":["2018xk03"],"award-info":[{"award-number":["2018xk03"]}]},{"name":"University Natural Science Research Program of Anhui Province","award":["ANR-10-LABX-005"],"award-info":[{"award-number":["ANR-10-LABX-005"]}]},{"name":"Key disciplines of Hefei University: Information and Communication Engineering","award":["22040421002"],"award-info":[{"award-number":["22040421002"]}]},{"name":"Key disciplines of Hefei University: Information and Communication Engineering","award":["KJ2021A0979"],"award-info":[{"award-number":["KJ2021A0979"]}]},{"name":"Key disciplines of Hefei University: Information and Communication Engineering","award":["2018xk03"],"award-info":[{"award-number":["2018xk03"]}]},{"name":"Key disciplines of Hefei University: Information and Communication Engineering","award":["ANR-10-LABX-005"],"award-info":[{"award-number":["ANR-10-LABX-005"]}]},{"name":"French national research agency (ANR) under the CaPPA","award":["22040421002"],"award-info":[{"award-number":["22040421002"]}]},{"name":"French national research agency (ANR) under the CaPPA","award":["KJ2021A0979"],"award-info":[{"award-number":["KJ2021A0979"]}]},{"name":"French national research agency (ANR) under the CaPPA","award":["2018xk03"],"award-info":[{"award-number":["2018xk03"]}]},{"name":"French national research agency (ANR) under the CaPPA","award":["ANR-10-LABX-005"],"award-info":[{"award-number":["ANR-10-LABX-005"]}]},{"name":"CPER ECRIN contracts","award":["22040421002"],"award-info":[{"award-number":["22040421002"]}]},{"name":"CPER ECRIN contracts","award":["KJ2021A0979"],"award-info":[{"award-number":["KJ2021A0979"]}]},{"name":"CPER ECRIN contracts","award":["2018xk03"],"award-info":[{"award-number":["2018xk03"]}]},{"name":"CPER ECRIN contracts","award":["ANR-10-LABX-005"],"award-info":[{"award-number":["ANR-10-LABX-005"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>The time constant selected for lock-in amplification (LIA) has a crucial impact on observed line shapes in laser heterodyne spectroscopy, in particular in the case of ground-based remote monitoring of trace gas in the atmospheric column using laser heterodyne radiometer (LHR). Conventional simulation could not allow validation of LHR spectra measured in a real and complex atmospheric environment exhibiting large temporal and spatial variability (humidity, temperature, pressure, etc) that impact significantly the measured LHR spectra profiles. High-precision spectral measurement is thus crucial to avoid any spectral distortion resulting from the measurement. In this paper, the impact of LIA time constant on spectral line shape is investigated for LHR operating in continuous laser tuning mode, based on analysis of laboratory heterodyne spectra, in terms of signal-to-noise ratio (SNR), line width broadening, absorption depth and line shift. With respect to the given frequency scanning speed in continuous mode and to the halfwidth of the absorption feature to scan, a reasonable scanning time \u0394Tscan, the time needed for scanning laser frequency through the halfwidth \u0394\u03bdHWHM of the absorption line, equal to or longer than 14 times of the LIA time constant \u03c4 is concluded in order to efficiently reduce the noise while without significant shift and distortion of the line shape. Experimental validation was carried out using a laser heterodyne absorption spectroscopy approach in the laboratory. Four different combinations of time constants \u03c4 and scanning time \u0394Tscan were used to record heterodyne spectra of a CH4 absorption line near 1242.00 cm\u22121 in continuous laser tuning mode. An optimal combination of a scanning time of 137 ms with a time constant of 1 ms was obtained. This optimal combination was used for ground-based measurements of CH4 and N2O in the atmospheric column by LHR. The extracted LHR spectrum is in good agreement with a referenced TCCON (Total Carbon Column Observing Network) FT-IR (Fourier-transform infrared) spectrum.<\/jats:p>","DOI":"10.3390\/rs14122923","type":"journal-article","created":{"date-parts":[[2022,6,19]],"date-time":"2022-06-19T21:19:26Z","timestamp":1655673566000},"page":"2923","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":15,"title":["Impact of Lock-In Time Constant on Remote Monitoring of Trace Gas in the Atmospheric Column Using Laser Heterodyne Radiometer (LHR)"],"prefix":"10.3390","volume":"14","author":[{"given":"Fengjiao","family":"Shen","sequence":"first","affiliation":[{"name":"School of Advanced Manufacturing Engineering, Hefei University, Hefei 230601, China"},{"name":"Laboratoire de Physico-Chimie de l\u2019Atmosph\u00e8re, Universit\u00e9 du Littoral C\u00f4te d\u2019Opale, 59140 Dunkerque, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gaoxuan","family":"Wang","sequence":"additional","affiliation":[{"name":"Laboratoire de Physico-Chimie de l\u2019Atmosph\u00e8re, Universit\u00e9 du Littoral C\u00f4te d\u2019Opale, 59140 Dunkerque, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2055-4057","authenticated-orcid":false,"given":"Zhengyue","family":"Xue","sequence":"additional","affiliation":[{"name":"Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tu","family":"Tan","sequence":"additional","affiliation":[{"name":"Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zhensong","family":"Cao","sequence":"additional","affiliation":[{"name":"Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xiaoming","family":"Gao","sequence":"additional","affiliation":[{"name":"Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6141-1039","authenticated-orcid":false,"given":"Weidong","family":"Chen","sequence":"additional","affiliation":[{"name":"Laboratoire de Physico-Chimie de l\u2019Atmosph\u00e8re, Universit\u00e9 du Littoral C\u00f4te d\u2019Opale, 59140 Dunkerque, France"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2022,6,18]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Lu, X., Huang, Y., Wu, P., Liu, D., Ma, H., Wang, G., and Cao, Z. 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