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Laser spectroscopy provides many possibilities for multi-disciplinary applications in environmental monitoring, in the ecological field, for food safety investigations, and in biomedicine. The paper gives several examples of the power of multi-disciplinary applications of laser spectroscopy as pursued in our research group. The studies utilize mostly similar and widely applicable spectroscopic approaches. Air pollution and vegetation monitoring by lidar techniques, as well as agricultural pest insect monitoring and classification by elastic scattering and fluorescence spectroscopy are described. Biomedical aspects include food safety applications and medical diagnostics of sinusitis and otitis, with strong connection to the abatement of antibiotics resistance development.
© 2016 Optical Society of America
1. Introduction
The fast development of laser spectroscopic techniques has brought about a revolution in optical spectroscopy, both regarding fundamental science applications and numerous application fields. There are more than a dozen Nobel Prize winners related to laser spectroscopy [1], mostly addressing fundamental aspects, such as high-resolution spectroscopy, cooling and trapping, quantum optics, Bose-Einstein condensation, etc. Application fields relate, e.g., to energy, environment, cultural heritage, ecology, pharmacy, food safety and medicine. Such applications have developed swiftly and are covered and high-lighted in numerous publications, such as [2–14]. High selectivity, high sensitivity, non-intrusiveness and even remote sensing, as well as real-time data availability are all attractive features of the technology. Amazingly, frequently very similar experimental techniques can be applied to seemingly quite different fields, a feature which stimulates cross-disciplinary research. The first author has been involved in such research endeavors for the last 40 years, activities which are briefly described in reviews such as [15–26]. Based on a recent overview presentation at a major cross-disciplinary meeting [27], we here give some examples from ongoing research, with an emphasis on activities in a new laboratory setting in South China. We will successively address environmental, ecological, food safety and biomedical applications, and conclude with some reflections.
2. Environmental applications
Much focus has recently been put on environmental issues, related to climate change [28], air and water pollution, etc. Clearly, science is of paramount importance to guide political decision making; a good example being the issue of polar ozone depletion, where the scientific studies, awarded by the 1995 Nobel Prize in Chemistry to P. J. Crutzen, M. J. Molina and F. Sherwood Rowland (see, e.g. [29,1]) led to actions [30] to curb an alarming development. Rapidly developing economies, such as the ones in China and India, are particularly vulnerable to environmental problems, well recognized by the authorities and now being addressed.
Adequate monitoring techniques are very important for assessing the situation and evaluating the effect of countermeasures. Optical remote sensing has the potential for fast coverage of large areas. Land resource utilization has been much studied by satellite techniques using reflectance spectroscopy [31,32] and atmospheric pollution can be monitored by high-spectral resolution satellite imaging [33], which is a variety of differential optical absorption spectroscopy (DOAS) [34,35] and by active laser techniques, both in the long-path absorption [36] and laser radar (lidar) [37,38] configuration. Mobile measurements are convenient for accessing local environmental issues. We have constructed a mobile platform for optical measurements on site, in particular for laser-radar (lidar) measurements, also with the differential absorption lidar variety [39]. The development is based on experience accumulated by the Lund university group [40], as also applied on the Chinese scene [41–45]. Figure 1 shows a lay-out of the system, and photographs of its appearance. The system is equipped with a main receiving Newtonian telescope of 40 cm diameter and an additional 30 cm telescope, both vertically looking and with roof-top folding mirrors for remote target selection.
Fig. 1 New mobile optical remote sensing mobile laboratory, constructed at South China Normal University. (a) General lay-out of the system. (b) Photograph of the system during a recent field experiment at Henan Agricultural University, Zhengzhou, China. (c) Photograph of the system interior, with operators (two of the co-authors) in the back-ground, transmitter lasers to the right, and optical telescope arrangements in the foreground.
The system has already been used in several applications, including monitoring of air pollutants and laser-induced fluorescence from remotely located solid samples, such as vegetation and minerals. Figure 2 shows data for range-resolved atomic mercury assessment performed with the differential absorption lidar (DIAL) technique. Tunable laser radiation at the mercury absorption line close to 254 nm (λon) and at a close-by reference wavelength (λoff) were generated in alternating laser shots at a repetition rate of 20 Hz, as generated by a frequency-doubled dye laser, pumped by a high-energy frequency-tripled Nd:YAG laser. The measurements were performed with the laser beam directed at a slant angle of about 12 degrees. Figure 2(a) shows the slightly sloping DIAL curve, obtained by dividing the lidar return signals for the λon and the λoff wavelengths, while Fig. 2(b) presents correspondingevaluated concentrations of mercury at different height intervals. Values are low, reflecting the fact that rain had occurred preceding the measurements, and concentrations are highest close to the ground. A range beyond 1.5 km can be achieved for mercury, which apart from being a serious environmental pollutant, related to waste incineration, coal-fired power plants and chlor-alkali industries, also is a very interesting geophysical tracer gas, with possible applications within ore prospecting etc [46]. Planned activities regarding atmospheric mercury monitoring include mining areas in the Guizhou province, and studies related to archeology, in particular at the Xi’an emperor Qin’s tomb next to the Terracotta Army site. For pollutant gases, such as sulfur dioxide, absorbing at a more easily attained UV wavelength around 300 nm, high laser outputs are available and measuring ranges go beyond 5 km.
Fig. 2 (a) Range-resolved differential optical absorption curve of atomic mercury recorded with the South China Normal University mobile laser radar system on August 22, 2015 in Guangzhou. Measurements were alternately performed on the mercury absorption line close to 254 nm and at a neighboring non-absorbing wavelength. The lidar back-scattering curves, basically featuring a 1/r2 intensity fall-off (r is the distance) were subsequently divided to yield the curve displayed. An expanded view is shown in the inset. If no mercury was present, the division would yield 1.00 at all ranges, since the curves would be identical. However, a slightly sloping curve is obtained due to mercury absorption, as is more clearly seen in the expanded view in the inset. The decrease over a range interval yields the corresponding range-resolved mercury concentration values, basically using the Beer-Lambert law. (b) Evaluated height resolved concentrations of atomic mercury during a 6 hours long time period. Considering that the measurements were performed at a slant angle of about 12 degrees, the height intervals are A: 41-83 m, B: 83-124 m, C: 124-166 m, D: 166-207 m, E: 207-249 m, and F: 249-291 m.
Likewise, the system can be used for monitoring laser-induced fluorescence remotely at ranges of the order of 100 m. Fluorescence lidar is applicable for monitoring water and vegetation [22]. The possibilities to use vegetation fluorescence for monitoring environmental stress have been much investigated; see, e.g [47]. There are also interesting applications to the monitoring of surfaces of cultural heritage buildings [20]. Figure 3 shows recordings of laser-induced fluorescence of Chinese marble samples (Dali stones) which we studied at a distance of 30 meters using dye laser excitation at 300 nm and collection of fluorescence light with the lidar telescope followed by spectral analysis. Fluorescence of minerals is mainly due to enclosed trace elements, and the spectral signatures can be used for determination of geographical origin, and be of assistance in e.g., restoration activities [20].
Fig. 3 Laser-induced fluorescence of Chinese marble samples recorded by fluorescence lidar techniques at a distance of 30 m. The samples were illuminated by a dye laser, with the output frequency-doubled to 300 nm. The spectra were recorded with the displayed very high signal-to- noise ratio using 200 laser pulses at 300 nm, each with an energy of about 15 mJ (10 s integration). A certified tungsten standard lamp (Labsphere, IES 1000) was used to calibrate the spectral sensitivity.
3. Ecological applications
Ecology describes the complex interaction between fauna, flora and humans. Ecological aspects receive increasing attention also by the general public, considering biological diversity also related to agriculture and food production. Optical spectroscopy is finding increasing applications in the ecological field. Insects are the class of animals with the greatest number of species. Lidar techniques are now emerging to complement radar-based insect remote sensing [48], with a first example of detection of hidden explosive mines through elastic lidar mapping of specially trained honey bees [49,50]. Elastic scattering techniques, also able to detect wing- beat frequencies and overtones for species identification [21,51] can be complemented with fluorescence detection [52,42].
Insects can even be effectively optically monitored without lasers, just using daytime strong scattering of sunlight from insects, which are observed with a small field-of-view optical telescope against a back-ground, which is arranged as dark as possible [53]. By reading out, at a high sampling rate, the reflectance spectrum from a compact spectrometer coupled to the telescope, information on species and gender can be obtained. Using such passive, dark-field techniques, wing-beat frequencies and overtones can also be obtained. The control of agricultural pest insects is of particular economic importance [54], and of course also strongly relates to the next section on food safety. Examples of Chinese agricultural insects (female and male specimen) are given in Fig. 4, which also shows a photograph of a dark-field remote insect monitoring set-up recently used at the Henan Agricultural University, Zhengzhou.
Fig. 4 Photographs of Chinese agricultural pests, and experimental set-up for dark-field insect monitoring at the Henan Agricultural University, Zhengzhou, China.
Figure 5 presents a time resolved recording of scattered light from an insect released into the field-of-view of a compact laboratory set-up for measurements of characteristic agricultural insect wing-beat frequencies. In this measurement, the insect was illuminated with a strong lamp and observed against a black back-ground. The figure shows the scattered intensity, as well as the evaluated Fourier transform of the data.
Fig. 5 Wing-beat frequency determination for a Hymenia recurvalis (Fabricius) released into a compact laboratory measurement system field-of-view. The figure shows the time-resolved recorded data and the corresponding Fourier transform, exhibiting overtones of the 62 Hz fundamental frequency.
It should be noted, that optical remote sensing techniques, including fluorescence lidar, can in similar ways be applied to the monitoring of migrating birds [55,56].
4. Food monitoring applications
Food safety is an area of increasing attention by the general public and authorities as well. The handling of agricultural products, regarding the use of pesticides, food additives, and occasional deliberate addition of dangerous substances to attain higher commercial value are all issues of serious concern. Likewise, the excessive use of antibiotics in husbandry contributes to the alarming development of antibiotics resistance, to be further discussed in the next section. Huge amounts of food are also destroyed because of inadequate handling and packaging. The purpose of packaging is frequently to provide a low-oxygen atmosphere to increase shelf-life of the products. The food industry is increasingly using modified atmosphere packaging (MAP) or controlled atmosphere (CA) storage [57,58]. Non-intrusive optical monitoring techniques based on spectroscopy have recently been introduced for assessing the status of food stuffs and packed foods (see, e.g., [59,60]). We are now pursuing a food safety research program on the Chinese scene, where such issues are frequently highlighted. Fruit quality and handling in view of the special perishable nature of such products is of special interest. We have studied the ripening and maturing of tropical fruits [61] by a combination of reflectance, fluorescence and gas in scattering media absorption spectroscopy (GASMAS [62,19], to be described further below). We here illustrate reflectance and fluorescence spectroscopy in the study of fruits by an example in Fig. 6, showing spectra of ripe guava and orange fruits (green and yellow/orange, respectively), the former having strong chlorophyll absorptive imprints in the 600-700 nm spectral region and prominent fluorescence signals at 690 and 735 nm (also due to chlorophyll), while the latter largely lacks such features. We note that the 690 nm fluorescence peak falls at a wavelength of strong absorption, leading to self-absorption of emitted light when the chlorophyll concentration increases. Thus, the relative intensities of the 690 and 735 nm peaks can be used to estimate the concentration of the pigment. While this is a pedagogical and dramatic demonstration of obvious features, even slight differences in spectral signatures revealing features of interest can be extracted using powerful multivariate analysis techniques [63,64], which are also extremely useful in data processing in the other applied spectroscopy fields discussed in the present paper.
Fig. 6 Measured reflectance and fluorescence spectra of ripe guava (green line) and orange fruits (orange line).
As mentioned, non-intrusive monitoring of gases inside foods and food packages is important. However, such materials are strongly scattering, which has strong consequences when quantitative optical measurements of gas concentrations are attempted. Basically, the path length of the probing light is not defined, but a distribution of short and long distances isobtained, making the use of the Beer-Lambert relation challenging. The GASMAS technique, already mentioned, was developed for such applications [19,65]. The method utilizes the fact that the absorptive imprints of free gases are typically 10,000 times narrower than those of condensed materials. Using tunable semiconductor laser spectroscopy combined with sensitive wavelength modulation spectroscopy (WMS), faint gas absorption imprints can be detected in the diffusely emerging light from the scattering gas-containing sample (see, e.g [66].). Using lock-in detection, frequently a signal resembling the second derivative of the absorption is obtained as shown in Fig. 7 for the case of oxygen recording around 760 nm in Chinese food packages. GASMAS signals are frequently expressed as Leq, corresponding to the equivalent path length in a non-scattering environment with well-defined gas concentration, giving rise to the same absorptive imprint. The relevant line-shape for the curve to be fitted to the experimental data is obtained by signal recording under ideal conditions in free air with adequate path length. The fitting amplitude parameter yields the Leq value. Figure 7(a) shows the raw signal from an intact bread package, while Fig. 7(b) shows the time development of the signal (the Leq value) after perforation of the package. Likewise, Fig. 7(c) shows a raw GASMAS signal for an intact milk package, while Fig. 7(d) displays the corresponding time development of Leq as in 7(b), but now for the milk package being perforated with a very small hole. Since the package is fixed all the time, the geometry is the same and thus the effective path length of the light through the gas. The time development is thus governed by the gas concentration in the package headspace only. Since we know that it will be 21% after the perforation we can deduce that it was about 9 and 16 percent, respectively, before the perforation of the packages. After such calibration numerous intact samples can be studied with regard to gas content. Non-intrusive GASMAS measurements on packages are reported in [67].
Fig. 7 GASMAS data for monitoring of food packages. A transition at about 760 nm (part of the oxygen A-band, also giving rise to a prominent terrestrial Fraunhofer line) was employed. (a) Raw GASMAS second-derivative WMS signal of oxygen in an intact bread package. (b) Oxygen signal amplitude followed during about 10 hours for the same bread package, which was perforated after about 1 hour. (c) Raw GASMAS signal for oxygen in an intact milk package. (d) Oxygen signal amplitude followed during 9 hours for the same milk package, being perforated after about 1 hour with a very small puncture.
A further example of GASMAS measurements, relating to bread, is shown in Fig. 8, where dough fermentation, with generation of carbon dioxide by the action of yeast is shown. Actually, water vapor is measured using an absorption line close to 935 nm, with a signal related to the gas volume (a moist sample exhibits 100% humidity in the gas enclosures, and the concentration of the vapor is determined by the temperature only [68,25]). It is noted, that the dough expands between the fixed containing glass plates, and the rising stops after about 1.5 hours, as monitored by water vapor signals.
Fig. 8 Study of the bread fermentation process with gas generation using GASMAS. The gas generated is carbon dioxide, but the voids generated also contain saturated water vapor. The water vapor signal measured at about 935 nm is used to monitor the expansion of the dough.
Oxygen content inside fresh fruits is also of considerable interest in monitoring the progress of ripening and the post-harvest condition. Such studies of tropical fruits were included in [61]. We have also investigated the action of the fruit skin in regulating the oxygen contents in the fruit [69], and an example from further studies is given in Fig. 9. Fruit in intact shape and after peeling were stored in plastic bags filled with pure oxygen or nitrogen, and the gas diffusion to a steady-state condition was followed after bag perforation. It is foundthat guava, being a tropical fruit, exhibits a different behavior from apple, being a temperate fruit. We have also performed diffusion studies of more well-defined samples, such as ceramics. The influence of porosity and presence of moisture was explored in [70], where we also found that the gas diffusion curve closely follows an exponential function. Generally speaking, the GASMAS technique can with simple equipment provide much information on diffusion processes in translucent materials.
Fig. 9 Diffusion of free oxygen gas into an apple during studies of fruit gas exchange. After storage of the apple in a high-oxygen atmosphere, the return to ambient air conditions was found to occur with a time constant of 24 minutes in this particular case.
5. Biomedical applications
The field of biomedical optics is expanding very fast, as exemplified by the appearance of many new scientific journals covering the subject, numerous conferences and many comprehensive overviews; see, e.g [9–14]. The senior authors of this paper were very early engaged in this area (see, e.g [71,72]. Medical diagnostics is performed with various spectroscopic techniques utilizing reflectance, fluorescence, Raman and coherent Raman spectroscopy, as described, e.g., in [23,26]. There are also many laser-based therapeutics techniques, including photodynamic therapy (PDT), which is particularly related to spectroscopic aspects (see, e.g [73,74]. Fluorescence spectroscopy and imaging have been employed much for early detection of malignant tumors utilizing special tumor markers, but also relying on the tissue autofluorescence [23]. Reflectance properties can also be useful. To exemplify such applications, human skin, subject to trauma, has been studied in our group. Spectral imprints due to hemoglobin with main absorption around 400 nm and secondary absorption features at 540 and 580 nm occur and have various prominences as time lapses from the time of trauma. Studies of this kind can have important bearing on forensic science including child abuse investigations [75].
We have recently been involved in the utilization of the GASMAS technique for biomedical applications based on prior work at Lund University. That work included monitoring of gas in human sinus cavities for diagnostics of sinusitis [76–79]. The motivation is to provide a useful technique for correct characterization of disease, to help prevent the alarming development of antibiotic resistance [80], caused by heavy misuse. This is a world-wide problem, but of course especially urgent in countries, like China, where antibiotics normally could be obtained directly in pharmacies without prescription. It is well-known, that antibiotics are not effective on virus, only on bacteria, and still many viral infections are treated with this kind of medication. A clinical trial with GASMAS on 40 patients, which were remitted to CT imaging, showed a good agreement in characterizing if cavities were gas-filled or not, both regarding frontal and maxillary cavities [79]. Also the air-bearing structures behind the outer ears (mastoids) could be studied with similar techniques [81]. Our recent work has included a study of the reproducibility of sinus cavity signals over extended times in healthy volunteers [82]. It was found that the signals are quite stable and that a reliable back-ground level exists, from which pathological deviations would be detectable.
Our further studies include exploratory experiments [83] towards developing optical detection techniques for another very common infectious disease, for which antibiotics are routinely applied – otitis or middle-ear infection. The main challenge in studying presence or absence of gas behind the eardrum is that the detection must occur in direct back-scattering through the auditory channel, as indicated in Fig. 10(a). A strong optical background through reflection from the eardrum makes signal recovery from gas behind the membrane challenging. By special design of the optical probe we could, however, show in phantom experiments, that such signals can be detected, as shown in Figs. 10(b) and 10(c) [83]. We also point out, that the combination with reflectance spectroscopy, objectively measuring the redness of the eardrum, can be quite useful. We are now trying to develop a compact device for clinical use on patients, in particular children, who constitute the most vulnerable group for attracting this disease.
Fig. 10 Illustration on spectroscopy related to otitis detection. Measurements must be performed in backscattering geometry through the auditory channel as illustrated in (a). Backscattering measurements of gas behind a thin biological membrane performed on a fish swimming bladder, mimicking a human eardrum, show gas exchange when the membrane is perforated, as illustrated in (b) and (c).
A further aspect of biophotonics applications to children care is the monitoring of lung function in prematurely born neonates. The lungs develop late, and insufficient levels of surfactants in the alveoli cause them to malfunction causing the respiratory distress syndrome (RDS). GASMAS has the potential to reduce the use of ionizing radiation in the monitoring of the premature lungs as suggested in first investigations on full-size newborns [84].
5. Conclusion
We have demonstrated how several fields of major importance for human well-being can be studied by applied laser spectroscopy. Environmental, ecological, food-safety, and biomedical applications may seem diverse, but have much synergy regarding experimental techniques and general measurement strategy. The importance of cross-disciplinary scientific collaboration in solving urgent societal issues is stressed.
Acknowledgments
The authors are grateful for a fruitful collaboration with Lund University, Sweden, and with Chinese partners, including Henan Agricultural University, Zhengzhou, as mediated by Prof. Jiandong Hu. The kind and persistent support by Prof. Sailing He is much appreciated. This work was financially supported by a Guangdong Province Innovation Research Team Program (No. 201001D0104799318), the Swedish Research Council and the Knut and Alice Wallenberg Foundation.
References and links
2. S. Svanberg, Atomic and Molecular Spectroscopy – Basic Aspects and Practical Applications, 4th ed. (Springer, 2004).
3. M. Sigrist, ed., Air Monitoring by Spectroscopic Techniques (John Wiley & Sons, 1994).
4. T. Fujii and T. Fukuchi, eds., Laser Remote Sensing (CRC Press, 2005).
5. P. Werle, F. D’Amato, and S. Viciani, “Tunable diode laser spectroscopy: principles, performance and perspectives,” in Lasers in Chemistry, M. Lackner, ed. (Wiley-VCH, Weinheim 2008).
6. M. Lackner, “Tunable diode laser spectroscopy (TDLAS) in the process industries – a review,” Rev. Chem. Eng. 23, 65–147 (2011).
7. J. Hodgkinson and R. P. Tatam, “Optical gas sensing: a review,” Meas. Sci. Technol. 24(1), 012004 (2013). [CrossRef]
8. M. Baudelet, ed., Laser Spectroscopy for Sensing: Fundamentals, Techniques and Applications (Woodhead Publishing, Cambridge 2013).
9. R. W. Waynant, ed., Lasers in Medicine (CRC, Baton Rouge 2002).
10. J. G. Fujimoto and D. L. Farkas, eds., Biomedical Optical Imaging (Oxford University, 2009).
11. J. Popp, V. V. Tuchin, A. Chiou, and S. H. Heinemann, eds., Handbook of Biophotonics, Volumes 1–3 (Wiley-VCH, 2011).
12. D. A. Boas, C. Pitris, and N. Ramanujam, Handbook of Biomedical Optics (CRC, 2011).
13. H. Jelinkova, ed., Lasers for Medical Applications: Diagnostics, Therapy and Surgery (Woodhead Publishing, 2013).
14. U. S. Dimish and M. Olivo, eds., Frontiers in Biophotonics for Translational Medicine (Springer, 2015).
15. S. Svanberg, “Laser spectroscopy applied in energy, environmental and medical research,” Appl. Phys. B 46(3), 271–282 (1988). [CrossRef]
16. S. Svanberg, “Geophysical gas monitoring using optical techniques: volcanoes, geothermal fields and mines,” Opt. Lasers Eng. 37(2-3), 245–266 (2002). [CrossRef]
17. M. Andersson, R. Grönlund, L. Persson, M. Sjöholm, K. Svanberg, and S. Svanberg, “Laser spectroscopy of gas in scattering media at scales ranging from kilometers to millimeters,” Laser Phys. 17(7), 893–902 (2007). [CrossRef]
18. S. Svanberg, “Laser based diagnostics - from cultural heritage to human health,” Appl. Phys. B 92(3), 351–358 (2008). [CrossRef]
19. S. Svanberg, “Gas in scattering media absorption spectroscopy – from basic studies to biomedical applications,” Laser Photonics Rev. 7(5), 779–796 (2013). [CrossRef]
20. V. Raimondi, G. Cecchi, D. Lognoli, L. Palombi, R. Grönlund, A. Johansson, S. Svanberg, K. Barup, and J. Hällström, “The fluorescence LIDAR technique for the remote sensing of photoautotrophic biodeteriogens on outdoor cultural heritage: a decade of in situ experiments,” Int. Biodeter. Biodegr. 63(7), 823–835 (2009). [CrossRef]
21. M. Brydegaard, A. Gebru, and S. Svanberg, “Super resolution laser radar with blinking atmospheric particles – application to interacting flying insects,” Prog. Electromagnetics Res. 147, 141–151 (2014). [CrossRef]
22. S. Svanberg, “Fluorescence Spectroscopy and Imaging of Lidar Targets,” Chap. 7 in [4], pp. 433–467. [CrossRef]
23. S. Andersson-Engels, K. Svanberg, and S. Svanberg, “Fluorescence Imaging in medical diagnostics,” Chap. 10 in [10], pp. 265–305.
24. K. Svanberg and S. Svanberg, “Monitoring of free gas in-situ for medical diagnostics using laser spectroscopic techniques,” Chap. 10 in [14], pp. 307–321. [CrossRef]
25. S. Svanberg, “Gas in Scattering Media Absorption Spectroscopy,” in Encyclopedia of Analytical Chemistry, M. Sigrist, ed. (John Wiley & Sons, 2014).
26. S. Svanberg, “Laser Spectroscopy in Medical Applications,” Chap. 10 in [13], pp. 286–324.
27. S. Svanberg, “Laser spectroscopy applied to environmental, ecological and medical research,” Plenary talk at Optics and Photonics for Energy and the Environment, Suzhou, China, 2–5 November 2015, ISBN: 978–1-55752–002–9. [CrossRef]
28. G. Myhre, D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura, and H. Zhang, “Anthropogenic and natural radiative forcing,” In Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, T.F. Stocker, D. Qin, G.-K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex, and P. M. Midgley, eds. (Cambridge University, Cambridge, United Kingdom and New York, NY, USA 2013).
29. M. J. Molina, “Polar ozone depletion,” in Nobel Lectures, Chemistry 1991–1995, Bo G. Malmström, ed. (World Scientific Publishing Co., Singapore, 1997).
30. C. A. Ennis, Coordinating editor, World Meteorological Organization Global Ozone Research and Monitoring Project - Report No. 55 (WMO 2014).
31. B. F. Wu, R. Gommes, M. Zhang, H. W. Zeng, N. N. Yan, W. T. Zou, Y. Zheng, N. Zhang, S. Chang, Q. Xing, and A. van Heijden, “Global crop monitoring: a satellite-based hierarchical approach,” Remote Sens. 7(4), 3907–3933 (2015). [CrossRef]
32. N. G. McDowell, N. C. Coops, P. S. A. Beck, J. Q. Chambers, C. Gangodagamage, J. A. Hicke, C. Y. Huang, R. Kennedy, D. J. Krofcheck, M. Litvak, A. J. H. Meddens, J. Muss, R. Negrón-Juarez, C. Peng, A. M. Schwantes, J. J. Swenson, L. J. Vernon, A. P. Williams, C. Xu, M. Zhao, S. W. Running, and C. D. Allen, “Global satellite monitoring of climate-induced vegetation disturbances,” Trends Plant Sci. 20(2), 114–123 (2015). [CrossRef] [PubMed]
33. C. Liu, S. Beirle, T. Butler, P. Hoor, C. Frankenberg, P. Jöckel, M. Penning de Vries, U. Platt, A. Pozzer, M. G. Lawrence, J. Lelieveld, H. Tost, and T. Wagner, “CO profiles from SCIAMACHY observations using cloud slicing and comparison with model simulations,” Atmos. Chem. Phys. 14(3), 1717–1732 (2014). [CrossRef]
34. U. Platt and J. Stutz, Differential Optical Absorption Spectroscopy - Principles and Applications (Springer, Berlin, 2008).
35. H. Edner, P. Ragnarson, S. Spännare, and S. Svanberg, “Differential optical absorption spectroscopy (DOAS) system for urban atmospheric pollution monitoring,” Appl. Opt. 32(3), 327–333 (1993). [CrossRef] [PubMed]
36. X. J. Cui, C. Lengignon, W. Tao, W. X. Zhao, G. Wysocki, E. Fertein, C. Coeur, A. Cassez, L. Croize, W. D. Chen, Y. J. Wang, W. J. Zhang, X. M. Gao, W. Q. Liu, Y. J. Zhang, and F. Z. Dong, “Photonic sensing of the atmosphere by absorption spectroscopy,” J. Quant. Spectrosc. Radiat. Transf. 113(11), 1300–1316 (2012). [CrossRef]
37. S. Svanberg, “LIDAR,” in Springer Handbook of Lasers and Optics, 2nd ed., F. Träger, ed. (Springer, 2012), pp. 1146–1169.
38. W. Q. Liu, Z. Y. Chen, P. H. Xie, J. G. Liu, and T. S. Zhang, “A comprehensive research of atmospheric haze by optical remote sensing in Central China Region (CCR),” in Current Air Quality Issues, F. Nejadkoorki, ed. (InTech, 2015), pp. 251–274.
39. S. Svanberg, “Differential absorption lidar (DIAL),” Chap. 3 in [3], pp. 85–161.
40. P. Weibring, H. Edner, and S. Svanberg, “Versatile mobile lidar system for environmental monitoring,” Appl. Opt. 42(18), 3583–3594 (2003). [CrossRef] [PubMed]
41. Z. G. Guan, L. Mei, P. Lundin, G. Somesfalean, and S. Svanberg, “Vertical lidar sounding of air pollutants in a major Chinese city,” Appl. Phys. B 101, 465–470 (2010). [CrossRef]
42. L. Mei, Z. G. Guan, H. J. Zhou, J. Lv, Z. R. Zhu, J. A. Cheng, F. J. Chen, C. Löfstedt, S. Svanberg, and G. Somesfalean, “Agricultural pest monitoring using fluorescence lidar techniques,” Appl. Phys. B 106(3), 733–740 (2011). [CrossRef]
43. L. Mei, Z. G. Guan, G. Somesfalean, and S. Svanberg, “Laser-induced fluorescence monitoring of Chinese Longjing tea,” Proc. SPIE 8531, 85311T (2012). [CrossRef]
44. L. Mei, G. Y. Zhao, and S. Svanberg, “Differential absorption lidar system employed for background atomic mercury vertical profiling in South China,” Opt. Lasers Eng. 55, 128–135 (2014). [CrossRef]
45. G. Y. Zhao, X. X. Wu, M. Lian, and S. Svanberg, “Lidar monitoring of atmospheric atomic mercury and sulfur dioxide in Guangzhou, China,” in Proc. PIERS,Guangzhou, 2014, pp. 2711–2714.
46. J. H. McCarthy, Jr., W. W. Vaughn, R. E. Learned, and J. L. Meuschke, “Mercury in soil gas and air - A potential tool in mineral exploration,” Geological Survey Circular 609 (US Geological Survey, 1969).
47. H. K. Lichtenthaler and U. Rinderle, “The role of chlorophyll fluorescence in the detection of stress in plants,” CRC Crit. Rev. Anal. Chem. 19(4), S29–S85 (1988). [CrossRef]
48. V. A. Drake and D. R. Reynolds, Radar Entomology: Observing Insect Flight and Migration (CABI, 2012).
49. J. Shaw, N. Seldomridge, D. Dunkle, P. Nugent, L. Spangler, J. Bromenshenk, C. Henderson, J. Churnside, and J. Wilson, “Polarization lidar measurements of honey bees in flight for locating land mines,” Opt. Express 13(15), 5853–5863 (2005). [CrossRef] [PubMed]
50. E. S. Carlsten, G. R. Wicks, K. S. Repasky, J. L. Carlsten, J. J. Bromenshenk, and C. B. Henderson, “Field demonstration of a scanning lidar and detection algorithm for spatially mapping honeybees for biological detection of land mines,” Appl. Opt. 50(14), 2112–2123 (2011). [CrossRef] [PubMed]
51. M. Brydegaard, A. Merdasa, A. Gebru, H. Jayaweera, and S. Svanberg, “Realistic instrumentation platform for active and passive optical remote sensing,” Appl. Spectrosc.0003702815620564 (2016), doi:. [CrossRef] [PubMed]
52. Z. Guan, M. Brydegaard, P. Lundin, M. Wellenreuther, A. Runemark, E. I. Svensson, and S. Svanberg, “Insect monitoring with fluorescence lidar techniques: field experiments,” Appl. Opt. 49(27), 5133–5142 (2010). [CrossRef] [PubMed]
53. A. Runemark, M. Wellenreuther, H. Jayaweera, S. Svanberg, and M. Brydegaard, “Rare events in remote dark field spectroscopy: an ecological case study of insects,” IEEE JSTQE 18, 1573–1582 (2011).
54. H. van Emden, Handbook of Agricultural Entomology (Wiley-Blackwell, 2013).
55. P. Lundin, P. Samuelsson, S. Svanberg, A. Runemark, S. Åkesson, and M. Brydegaard, “Remote nocturnal bird classification by spectroscopy in extended wavelength ranges,” Appl. Opt. 50(20), 3396–3411 (2011). [CrossRef] [PubMed]
56. M. Brydegaard, P. Samuelsson, M. W. Kudenov, and S. Svanberg, “On the exploitation of mid-infrared iridescence of plumage for remote classification of nocturnal migrating birds,” Appl. Spectrosc. 67(5), 477–490 (2013). [CrossRef] [PubMed]
57. I. J. Church and A. L. Parsons, “Modified atmosphere packaging technology: a review,” J. Sci. Food Agric. 67(2), 143–152 (1995). [CrossRef]
58. A. K. Thompson, Controlled Atmosphere Storage of Fruits and Vegetables, 2nd ed., (CABI, 2010)
59. M. Lewander, Z. G. Guan, L. Persson, A. Olsson, and S. Svanberg, “Food monitoring based on diode laser gas spectroscopy,” Appl. Phys. B 93(2-3), 619–625 (2008). [CrossRef]
60. M. Lewander, P. Lundin, T. Svensson, S. Svanberg, and A. Olsson, “Non-intrusive measurements of headspace gas composition in liquid food packages made of translucent materials,” Packag. Technol. Sci. 24(5), 271–280 (2011). [CrossRef]
61. H. Zhang, J. Huang, T. Li, X. Wu, S. Svanberg, and K. Svanberg, “Studies of tropical fruit ripening using three different spectroscopic techniques,” J. Biomed. Opt. 19(6), 067001 (2014). [CrossRef] [PubMed]
62. M. Sjöholm, G. Somesfalean, J. Alnis, S. Andersson-Engels, and S. Svanberg, “Analysis of gas dispersed in scattering media,” Opt. Lett. 26(1), 16–18 (2001). [CrossRef] [PubMed]
63. A. C. Rechner, Methods of Multivariate Analysis (Wiley, New York 2002).
64. T. W. Anderson, An Introduction to Mulitvariate Statistical Analysis, 3rd ed., (Wiley, Hoboken, N.J. 2013).
65. L. Mei, G. Somesfalean, and S. Svanberg, “Pathlength determination for gas in scattering media absorption spectroscopy,” Sensors (Basel) 14(3), 3871–3890 (2014). [CrossRef] [PubMed]
66. L. Mei and S. Svanberg, “Wavelength modulation spectroscopy--digital detection of gas absorption harmonics based on Fourier analysis,” Appl. Opt. 54(9), 2234–2243 (2015). [CrossRef] [PubMed]
67. H. Zhang, H. Y. Lin, T. Q. Li, Z. Duan, K. Svanberg, and S. Svanberg, “Non-invasive optical detection of oxygen content in food packages using gas in scattering media absorption spectroscopy,” Acta Opt. Sin. 36(2), 0230005 (2016). [CrossRef]
68. A. L. Buck, “New equations for computing vapor-pressure and enhancement factor,” J. Appl. Meteorol. 20(12), 1527–1532 (1981). [CrossRef]
69. J. Huang, H. Zhang, T. Q. Li, G. Y. Zhao, S. Svanberg, and K. Svanberg, “Studies of oxygen and oxygen exchange in fruits using gas in scattering media absorption spectroscopy,” in Proc. PIERS,Guangzhou, 2014, pp. 1251–1255.
70. H. Zhang and S. Svanberg, “Laser spectroscopic studies of gas diffusion in alumina ceramics,” Opt. Express (accepted).
71. J. Ankerst, S. Montán, K. Svanberg, and S. Svanberg, “Laser-induced fluorescence studies of hematoporphyrin derivative (HPD) in normal and tumor tissue of rat,” Appl. Spectrosc. 38(6), 890–896 (1984). [CrossRef]
72. S. Montán, K. Svanberg, and S. Svanberg, “Multicolor imaging and contrast enhancement in cancer-tumor localization using laser-induced fluorescence in hematoporphyrin-derivative-bearing tissue,” Opt. Lett. 10(2), 56–58 (1985). [CrossRef] [PubMed]
73. K. Svanberg, T. Andersson, D. Killander, I. Wang, U. Stenram, S. Andersson-Engels, R. Berg, J. Johansson, and S. Svanberg, “Photodynamic therapy of non-melanoma malignant tumours of the skin using topical delta-amino levulinic acid sensitization and laser irradiation,” Br. J. Dermatol. 130(6), 743–751 (1994). [CrossRef] [PubMed]
74. K. Svanberg, N. Bendsoe, J. Axelsson, S. Andersson-Engels, and S. Svanberg, “Photodynamic therapy: superficial and interstitial illumination,” J. Biomed. Opt. 15(4), 041502 (2010). [CrossRef] [PubMed]
75. L. L. Randeberg, A. M. Winnem, S. Blindheim, O. A. Haugen, and L. O. Svaasand, “Optical classification of bruises,” Proc. SPIE 5312, 54–64 (2004). [CrossRef]
76. L. Persson, K. Svanberg, and S. Svanberg, “On the potential for human sinus cavity diagnostics using diode laser gas spectroscopy,” Appl. Phys. B 82(2), 313–317 (2006). [CrossRef]
77. L. Persson, M. Andersson, M. Cassel-Engquist, K. Svanberg, and S. Svanberg, “Gas monitoring in human sinuses using tunable diode laser spectroscopy,” J. Biomed. Opt. 12(5), 054001 (2007). [CrossRef] [PubMed]
78. M. Lewander, Z. Guan, K. Svanberg, S. Svanberg, and T. Svensson, “Clinical system for non-invasive in situ monitoring of gases in the human paranasal sinuses,” Opt. Express 17(13), 10849–10863 (2009). [CrossRef] [PubMed]
79. M. Lewander, S. Lindberg, T. Svensson, R. Siemund, K. Svanberg, and S. Svanberg, “Clinical study assessing information on the maxillary and frontal sinuses using diode laser gas spectroscopy,” Rhinol. 50, 26–32 (2011).
80. H. Goossens, M. Ferech, R. van der Stichele, M. Elseviers, and ESAC Project Group, “Outpatient antibiotic use in Europe and association with resistance: a cross-national database study,” Lancet 365(9459), 579–587 (2005). [CrossRef] [PubMed]
81. S. Lindberg, M. Lewander, T. Svensson, R. Siemund, K. Svanberg, and S. Svanberg, “Method for studying gas composition in the human mastoid cavity by use of laser spectroscopy,” Ann. Otol. Rhinol. Laryngol. 121(4), 217–223 (2012). [CrossRef] [PubMed]
82. J. Huang, H. Zhang, T. Li, H. Lin, K. Svanberg, and S. Svanberg, “Assessment of human sinus cavity air volume using tunable diode laser spectroscopy, with application to sinusitis diagnostics,” J. Biophotonics 8(11-12), 985–992 (2015). [CrossRef] [PubMed]
83. H. Zhang, J. Huang, T. Li, S. Svanberg, and K. Svanberg, “Optical detection of middle ear infection using spectroscopic techniques: phantom experiments,” J. Biomed. Opt. 20(5), 57001 (2015). [CrossRef] [PubMed]
84. E. Krite Svanberg, P. Lundin, M. Larsson, J. Åkeson, K. Svanberg, S. Svanberg, S. Andersson-Engels, and V. Fellman, “Noninvasive monitoring of oxygen in the lungs of newborn infants by diode laser spectroscopy,” Pediatr. Res. (2016), doi:. [CrossRef]
