Spectroscopic measurements of volcanic gas emissions in the ultra-violet wavelength region [Elektronische Ressource] / put forward by Christoph Kern

Christoph Kern

Informations

• Publié par: ruprecht-karls-universitat_heidelberg
• Publié le: 01 janvier 2009
• Nombre de lectures: 29
• Langue: Deutsch
• Poids de l'ouvrage: 7 Mo

Extrait

Dissertation
submitted to the
Combined Faculties for the Natural Sciences and for Mathematics
of the Ruperto-Carola University of Heidelberg, Germany
for the degree of
Doctor of Natural Sciences












Put forward by
Dipl. Phys. Christoph Kern
Born in Mount Kisco, NY, USA

Oral examination: June 10, 2009





Spectroscopic measurements of volcanic gas emissions
in the ultra-violet wavelength region
















Referees: Prof. Dr. Ulrich Platt
Prof. Dr. Thomas Wagner


Spektroskopische Messungen von Vulkangasemissionen im ultra-violetten
Wellenlängenbereich
In dieser Dissertation wurden drei neue Fernerkundungsinstrumente gebaut und angewandt
um Vulkangasemissionen zu charakterisieren: ein passiver abtastender differentieller
optischer Absorptionsspektrometer (DOAS), ein aktives Langpfad DOAS Gerät, und eine
SO -Kamera. Mit dem passiven DOAS wurden Schwefeldioxid (SO ) Emissionsflüsse an 6 2 2
Vulkanen erfolgreich gemessen. Am Kilauea Vulkan (Hawaii) wurden z.B. im März 2008
erhöhte SO Emissionsflüsse entdeckt, ein Anzeichen für einen möglicherweise 2
bevorstehenden Vulkanausbruch. Dieser fand wenige Wochen später statt. Halogenchemie in
Vulkanfahnen wurde auch untersucht. So wurde z.B. Brommonoxid (BrO) am Stromboli
(Italien), Popocatépetl (Mexiko), und Masaya (Nicaragua) nachgewiesen. Durch die
erstmalige Anwendung eines aktiven DOAS Geräts auf Vulkanfahnen konnte BrO am
Masaya auch nachts quantifiziert werden. Ein deutlicher Tagesgang wurde gefunden in dem
die höchsten Konzentrationen mittags auftraten, während sie nachts unterhalb der
Nachweisgrenze lagen. Dieser Befund deutet auf eine photochemische Bildung von BrO in
Vulkanfahnen hin. Schließlich wurde ein Strahlungstransportmodel benutzt um die Wege von
Photonen in passiven Fernerkundungsmessungen zu simulieren. Die Ergebnisse zeigen, dass
eine ungenaue Beurteilung von Photonenwegen in Vulkanfahnen zu großen Fehlern in den
Messungen führen kann. Ein Korrekturalgorithmus wird vorgestellt, mit dem auch zum ersten
Mal Aerosolbedingungen in Vulkanfahnen durch DOAS Messungen bestimmt werden
können.

Spectroscopic measurements of volcanic gas emissions in the ultra-violet
wavelength region
In this thesis, three new remote sensing instruments were designed and applied to characterize
volcanic gas plumes: a passive scanning differential optical absorption spectrometer (DOAS),
an active Long-Path DOAS, and an SO -camera. Using the passive DOAS, sulfur dioxide 2
(SO ) emission fluxes were successfully quantified at 6 volcanoes. At Kilauea (Hawaii), e.g., 2
elevated fluxes were measured in March 2008, an indication of an upcoming eruption which
occurred just weeks later. Halogen chemistry in volcanic plumes was also studied. Bromine
monoxide (BrO) was positively detected at Stromboli (Italy), Popocatépetl (Mexico) and
Masaya (Nicaragua) volcanoes. By applying an active DOAS system to volcanoes for the first
time, BrO measurements were conducted at night at Masaya. A distinct diurnal cycle was
found in which the highest concentrations were present around local noon while they were
below the detection limit at night, a strong indication that BrO is photochemically formed in
volcanic plumes. Finally, radiative transfer modeling was used to simulate the optical paths of
photons during passive remote sensing measurements. The results show that an inaccurate
assessment of radiative transfer can induce large errors in these measurements. A correction
algorithm is presented that for the first time allows the retrieval of aerosol conditions in
volcanic plumes from DOAS measurements.
Table of Contents


1 INTRODUCTION ..................................................................................................................................... 11
2 THE IMPORTANCE OF VOLCANIC GAS EMISSIONS IN ATMOSPHERIC CHEMISTRY AND
VOLCANOLOGY .............................................................................................................................................. 17
2.1 THE IMPORTANCE OF VOLCANIC GAS EMISSIONS FOR ATMOSPHERIC CHEMISTRY ............................... 17
2.1.1 Atmospheric chemistry and transport ........................................................................................... 18
2.1.2 Volcanic gas composition.............................................................................................................. 21
2.1.3 The effects of volcanic eruptions on stratospheric chemistry and climate .................................... 22
2.1.4 of vouptions on tropospheric chemistry ........................................................ 24
2.2 THE IMPORTANCE OF GAS EMISSIONS IN VOLCANOLOGY AND VOLCANIC RISK ASSESSMENT .............. 32
2.2.1 SO emission fluxes ....................................................................................................................... 33 2
2.2.2 Relative halogen abundances........................................................................................................ 35
3 DIFFERENTIAL OPTICAL ABSORPTION SPECTROSCOPY ....................................................... 39
3.1 PRINCIPLES ......................................................................................................................................... 39
3.1.1 Atmospheric absorption spectroscopy........................................................................................... 39
3.1.2 Differential spectroscopy .............................................................................................................. 40
3.1.3 Mathematical description of the instrumental spectral processing............................................... 43
3.1.4 Evaluation procedure.................................................................................................................... 48
3.1.5 Error estimation............. 50
3.1.6 Detection limit............................................................................................................................... 53
3.2 MEASUREMENT CONCEPTS – ACTIVE DOAS ...................................................................................... 55
3.2.1 Active Long Path DOAS................................................................................................................ 57
3.2.2 Optical path length requirements in volcanic plumes................................................................... 57
3.2.3 Plume composition ratios.............................................................................................................. 59
3.3 MEASUREMENT CONCEPTS – PASSIVE DOAS..................................................................................... 62
3.3.1 Direct sun / solar occultation geometry ........................................................................................ 62
3.3.2 Scanning DOAS measurements of localized plumes using scattered solar radiation ................... 64
3.3.3 Mobile DOAS traverse method...................................................................................................... 69
3.3.4 Wind speed determination...... 72
3.3.5 Longitudinal diffusion along plume axis ....................................................................................... 75
3.3.6 Error sources in emission flux measurements............................................................................... 77
3.4 ADVANCED CONCEPTS FOR DATA RETRIEVAL 80
3.4.1 Wavelength dependent optical paths............................................................................................. 80
3.4.2 Non-commutative convolution....................................................................................................... 83
3.4.3 Instrument sensitivity..................................................................................................................... 86
3.4.4 Spectrometer stray light ................................................................................................................ 91
3.4.5 Temperature effects....................................................................................................................... 96
3.5 DEVELOPMENT OF DOAS INSTRUMENTATION FOR VOLCANIC GAS EMISSIONS MEASUREMENTS ...... 103
3.5.1 NOVAC mark II gas emissions monitoring instrument ............................................................... 103
3.5.2 Miniature Active Long Path DOAS 110



7
4 THE SO -CAMERA................................................................................................................................ 119 2
4.1 INTRODUCTION ................................................................................................................................. 119
4.2 MEASUREMENT PRINCIPLE................................................................................................................ 120
4.3 NORMALIZED OPTICAL DENSITY / APPARENT ABSORBANCE.............................................................. 123
4.4 CALIBRATION ISSUES 124
4.4.1 Incident spectral intensity ..............................