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A Graduate-Level Online Module for Teaching Remote Sensing of Tropospheric NO2 from Space A. Ladstätter-Weißenmayer and A. Richter Institute of Environmental Physics, University of Bremen, D-28334 Bremen, Germany J. P. Burrows Institute of Environmental Physics, University of Bremen, D-28334 Bremen, Germany; and Centre for Ecology and Hydrology, Wallingford, Oxfordshire, OX10 8BB, United Kingdom M. Kanakidou Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, GR-71003 Heraklion, Greece R. J. Law PerModum, Postfach CH-7155 Ladir, Switzerland T. Wagner Max Planck Institute for Chemistry, D-55128 Mainz, Germany Peter Borrell* P and PMB Consultants, Newcastle-under-Lyme, Staffordshire, ST5 2QJ, United Kingdom; *[email protected]

Using remote sensing instrumentation onboard orbiting satellites, it is now possible to obtain global information about pollutants in the troposphere and, in some cases, in the atmospheric boundary layer (1). Retrieving such tropospheric information from the satellite data is a large and growing task requiring much expertise before it can become fully operational. Thus, a growing number of research groups are involved in obtaining tropospheric data, validating and evaluating it, and using it, both to improve understanding of the global troposphere and to study the changes under the impact of human activities. The AT2 e-learning module, Remote Sensing of the Tropospheric NO2 from Space, was developed to provide an online introduction for graduate students in this area, and also to provide an online background for those interested in the possibilities of remote sensing of the troposphere from space. ACCENT-TROPOSAT-2 (AT2) is an integration task of ACCENT, the European Union (EU) network of excellence for atmospheric chemistry. AT2 brings together the European community of researchers in the field of satellite remote sensing of the troposphere to address the need for global information about trace atmospheric constituents. Its aim is to facilitate generation of tropospheric data products, to encourage their use for research in the medium term, and to indicate their potential use in the development of environmental policy (2). As part of the ACCENT Training and Education (T&E) activities, the AT2 group endeavored to develop the remote sensing module described here (3). The AT2 e-learning module could be termed an “interactive textbook” presenting the subject material to students and, by means of interactive exercises, allowing students to assess and to improve their comprehension of this material. It is designed to complement conventional textbooks and other learning materials. The educational aim of the module is to communicate an understanding of the role of NO2 in atmospheric chemistry (4) as well as the retrieval and use of NO2 observations from space (5–7). NO2 was chosen because: (i) it is an important natural trace substance and an anthropogenic pollutant; (ii) it can be readily detected in satellite spectra; and (iii) NO2 exists in the stratosphere and the troposphere. Thus all the important 750

retrieval steps, including stratosphere–troposphere separation, can be demonstrated. The module is intended for use by graduate students, and thus a graduate-level background in science is assumed. However, students often come from different disciplines (physics, chemistry, earth sciences, and mathematics, for example), and so the module is intended to familiarize graduate students with the basic science of a complex field. The module itself has been successfully tested in a workshop and in research groups throughout Europe. It is available online and access is free: see ref 8 for more details. The module fits well within the current thinking about “learning objects”, because it is a knowledge-based object that is “discoverable, modular, and interoperable”, or in another definition, “self-contained and re-usable” (9). We gained a great deal of experience in the development of the module, so it seemed worthwhile to communicate in this paper the lessons learned and to indicate the requirements needed to develop a successful module. Some pitfalls to avoid are also pointed out. These fit with the known demand for advice about “effective, time-efficient” ways of using modern aids to support student learning in higher education (10). Presenting the Material in the Module The approach used in the module includes two didactical aspects (11): presentation of information and education by training, and encouraging the students to test themselves and improve their own understanding of the material. The module presents the topic to students with a step-bystep introduction to using satellite observations to calculate NO2 distributions in the troposphere. The module shows how the results are derived from a real set of raw data observed by the satellite-borne instrument, and how these data are interpreted. In addition, it offers references and links for further reading. Accessibility From a system perspective, the project’s aim was to develop a highly interactive e-learning module that could operate as a

Journal of Chemical Education • Vol. 86 No. 6 June 2009 • www.JCE.DivCHED.org • © Division of Chemical Education

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stand-alone module. The module is designed to run in a up-todate Web browser and it consists of typical Web components— HTML files, JavaScript scripts, and cascading style sheet files. Unlike many other proprietary e-learning systems, it does not use plug-ins or require special code or languages. It requires no server-side “delivery” techniques, and can be delivered from a Web server or accessed by a network client from a file server. It is stand alone and can be stored on a CD-ROM or USB memory stick and used offline. It can also be integrated seamlessly into any of the major course management systems (CMS) such as Moodle or WebCT (Blackboard) without appreciable additional effort. As a stand-alone system using normal Web components, it is future-safe and completely portable. The AT2 module was created using the LexEOS e-learning system (12), which stores data in the form of XML files that are editable using a normal XML editor. The XML source files are freely available to authors and can be created and edited at will. Presenting the Scientific Content Construction of the module falls into two parts—study pages to present the scientific content, and exercises pages, with which students can test their knowledge. The original scientific content was delivered as a set of lecture slides; these slides were modified and augmented as the module developed. The initial task was to write a description for each slide, which is a demanding exercise in itself; as common experience bears out, some

lecture slides need only a short description, while others may require a considerable time to present. The scientific content is divided into three parts: (i) remote sensing; (ii) basics of atmospheric radiation transfer; and (iii) retrieval procedures (see Figure 1). This discussion can best be appreciated while also exploring the module online (8) in conjunction with reading this paper. The first chapter, Remote Sensing, deals with the importance of the nitrogen oxides, NOx (i.e., NO and NO2), and the use of satellite measurements in general. Different types of nitrogen compounds in the atmosphere—sources and sinks and their altitude and spatial distribution—are explained in more detail (4). Reactions of stratospheric as well as tropospheric NO2 are described using overviews, chemical equations, and explanatory text. Because distribution of NO2 in the troposphere is highly variable in space and time, the advantages of observing and measuring it using the tools of remote sensing from space are evident. As an example, a case study of biomass burning is presented to students who explore the topic step-by-step. Through the case study—which uses data from the GOME satellite instrument— students encounter information regarding the emission and distribution of trace gases, NO2, formaldehyde (HCHO), and ozone, O3 (see Figure 2) (13, 14). The module’s first section describes the satellite instruments GOME (15) and SCIAMACHY (16, 17), from which many of the current tropospheric measurements are made. GOME

Figure 1. Screenshot of the starting point for the AT2 e-learning module Remote Sensing of the Troposphere from Space. Three columns display in the browser window: the left shows the index and current position in the module; the middle has the main text and tutorial questions; and the right provides navigation links (only within the same level), some options, and exercise scores.

© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 86 No. 6 June 2009 • Journal of Chemical Education

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was launched in 1995 on satellite ERS-2 in a sun-synchronous, near-polar orbit at a mean altitude of 795 km. It measures the sunlight backscattered from Earth’s atmosphere and reflected by the surface at wavelengths of 240–790 nm with a spectral resolution of 0.2–0.4 nm. SCIAMACHY, a more elaborate instrument, was launched in 2002 with a primary mission to perform global measurements of trace gases in the troposphere and stratosphere. The solar radiation transmitted, backscattered, and reflected from the atmosphere is recorded at a better spatial resolution over the range 240–1700 nm with a spectral resolution of 0.2–1.5 nm, and in selected regions between 2000–2400 nm. SCIAMACHY has three different viewing geometries—nadir, limb, and sun–moon occultation—that yield total column values as well as distribution profiles in the stratosphere and (in some cases) the troposphere for trace gases and aerosols (16, 17). The module explains satellite-scanning concepts and techniques, including: polar, near-polar, and sun-synchronous orbits; swath; wavelength ranges; scan sequences; and different observing modes such as nadir, limb, and occultation mode and their measurement sequence (see Figure 3) (17). The second section introduces the basics of atmospheric radiation transfer and addresses the question “How do we use satellite measurements to determine tropospheric NO 2 columns?” To answer this question and to understand the background of the retrieval procedures of satellite-based data, an introduction to the concepts of electromagnetic radiation, radiative transfer, and the radiation transfer equation are given. Wavelength, radiance, and irradiance are defined, as well as the general terms and units commonly used in this field. Blackbody radiation, blackbody absorption, and Planck’s law are explained in more detail.

To understand the radiative transfer in the atmosphere, different processes such as absorption, scattering, and reflection have to be taken into account. The Beer–Lambert law is introduced along with Rayleigh and Mie scattering processes (events after which the scattered photons have the same wavelength but not the same direction as the original photon), together with Raman scattering (a scattering event after which the photons change their wavelength). Solar radiation reaching Earth’s surface is partly redirected back into the atmosphere by reflection, which depends on the surface albedo (reflectance), which in turn depends on surface characteristics. Thus the light finally reaching the spectrometer is determined by the radiative transfer of sunlight that falls on Earth and is multiply scattered in the atmosphere. The third section, Retrieval Procedures, explains the intricate process of data retrieval. Trace gases such as NO2 are detected by their absorption spectra and the concentration is determined by differential optical absorption spectroscopy (DOAS). The DOAS method (18) is explained both graphically in a step-by-step guide and, mathematically in a step-bystep presentation of the DOAS radiative transfer equation. Students are shown the way that the earthshine spectrum for each ground pixel is compared to the solar irradiance at the satellite and how a value for the concentration of NO2 in the tropospheric column above that ground pixel is derived. The whole process of analyzing the total vertical column, extracting the stratospheric part, and finally retrieving the tropospheric vertical column amount is explained with a sequence of retrieval steps that takes students through the complete retrieval process. Initial analysis of the data yields a so-called slant column density of NO2. This must be converted to the required vertical

Figure 2. Screenshot, Biomass Burning: A Case Study, from the AT2 e-learning module Remote Sensing of the Troposphere from Space. Note the other topics listed in the index on the left.

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column density by use of the air mass factor (AMF), which is based on radiative transfer calculations (19, 20). Important influences such as geometry, altitude, albedo, and wavelength are explained and illustrated by diagrams. Two common methods to eliminate the stratospheric column density from the total amount to yield the final tropospheric column densities are described: the reference sector method and the limb mode profile approach, together with their advantages and disadvantages (6, 21).

Figure 4 shows an example of the final outcome of such an analysis. One can readily see that the concentration of the air pollutant NO2 over China has increased in the period between the two sets of observations, while it remained the same over other regions, such as Japan. It should be noted that, as a teaching tool, the module itself does not provide access to real-time data, only to one selected example. Real-time data are available from different sources on the Web and links to these data sources are included in the module.

Figure 3. Screenshot, SunSynchronous Orbits, from the AT2 e-learning module Remote Sensing of the Troposphere from Space. Polar orbits and sun-synchronous, nearpolar orbits during Earth’s year are described in the section on satellite measurements.

Figure 4. Distributions of NO2 in the atmosphere over China in 2004 and 2007, constructed from observations with the SCIAMACHY instrument. For a more detailed study see ref 7.


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Testing Students’ Comprehension of the Module In order to verify the level of comprehension attained, the learning process is supported by about 70 interactive exercises that allow students to evaluate their understanding and comprehension of the material at each step. Given the advanced level of study at which the module was aimed, these exercises encompass conceptual as well as factual material. Here we discuss the structure and the scientific content to illustrate the level of the work and to indicate how the module was constructed. The potential advantage of e-learning over a static textbook is that students can be given the opportunity to test their own comprehension as they work their way through (10). Although the interactive exercises in the module test students’ understanding and knowledge, the exercises are not designed to be tests in the traditional sense. Students can repeat exercises as often as they wish and so improve their scores and understanding. Evaluation and Correction of Students’ Work A number of different exercise types are used in the module and they all have a standard procedure for the evaluation and correction of students’ work. At any time when working in an exercise—whether all questions have been answered or not— students can choose to evaluate their answers. Correct answers are marked in green, incorrect answers in red. When there are incorrect answers in the exercise students can try again, modifying the incorrect answers. Correct answers after the first attempt are marked in a pale green. Only a limited number of attempts is available. If the number of attempts is used up and there are still incorrect answers in the exercise, the correct answers are substituted, displayed in blue. An important principle of the module functionality is thus demonstrated: upon completion of an exercise, students are left with only correct answers on the screen. Exercise Types Six exercise types are used in the interactive sections of the AT2 e-learning module.

1. Gap-option exercises—Each gap to be filled can cycle through several alternatives of text or diagrams.

2. Category-marker exercises—A table of alternatives is provided that must be fitted to the several gaps in a text.

3. Multiple-choice exercises—One or more questions or statements together with the associated options are presented. The options are, in effect, interactive gaps that can be selected and deselected.

4. Gap-fill exercises—Contains a number of gaps and a table of items that can be put in the gaps. Items and gaps can be in any ratio.

5. Type-in exercises—The gaps display placeholders and students have to select and type into each gap (good for chemical formulas, etc.).

6. Annotated text—Contains a number of gaps, acting as annotation hot spots and not requiring input from the user. Clicking the gaps displays an associated annotation.

Each of these principal types has several variants. A common feature of these exercises is the use of “gaps” that require some input from users as an answer. Gaps need not only be text

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elements, they can be texts within images, images within texts, or images within images. Structurally, they can be incorporated into run-on text or organized in some way such as in tables or within mathematical expressions. Students can fill the gaps using either mouse or keyboard at will, which makes the system more accessible for people with disabilities. A detailed description of the exercise types is given in the online supplement of this paper. Scoring the Tests Although students can improve their scores by reworking an exercise, many like to have a record of their work. The module therefore offers a complete scoring system with the following features (see Figure 5):

• Scoring in the control panel, updated during the work

• Score tables that list the scores achieved in a group of exercises; each exercise is listed with the number of correct, “half-correct” (answers only correct after the first attempt), and incorrect answers it contains

• Saving and printing scores; scores are saved whenever the module is closed or refreshed

Help Systems While the module’s interface has been designed to be as intuitive as possible, a large range of context-related help is available. Exercises have help topics concerning their functionality, including features such as:

• Pop-up windows containing a guide for using the particular exercise type

• Information about particular functionalities—entering mathematical expressions, for example

• Content tips for the completion of the exercise

• Pop-up “tool tips” when the cursor is over that element

• Glossary definitions

Most of these features can be deactivated or re-activated at will. Course Management Environment The purpose of the AT2 module is to provide a variety of laboratories in different institutions in different countries with a course on remote sensing from space using real data from the satellites GOME and SCIAMACHY. Therefore it was best to have a stand-alone module not associated with a particular course management system. Nonetheless, the module has been constructed so that it can be integrated into Moodle and other course management systems, such as Blackboard and WebCT. We used an implementation within Moodle at our feedback workshop in order to collect opinions from the students and others testing the module. One could, in principle, integrate the module into a CMS to allow assessment of students, yet this defeats the philosophy of our approach, which is to encourage students to achieve comprehension of the material at an advanced level. Incorporating the module into a content management system might, however, provide a useful check on whether a student has actually addressed the material.


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Evaluation of the Module

As part of the development process, the module was tested in a classroom environment at a workshop held in Heraklion, Crete in June 2006. The “students” were about 30 colleagues, some senior, some postdoctoral, and some research students. Feedback was obtained with comments collected via the Moodle environment in which the module was installed on that occasion. While many suggestions were made for improvement— most of which have been implemented—the overall reaction was quite favorable. The module is now being used in teaching at the University of Bremen and is available for ad-hoc study in Crete and Heidelberg.

2. While a personal computer offers the possibility of numerous presentation effects, the aim is to produce an educational module rather than a “sound and light” show! It is easy to spend a large proportion of one’s resources on clever effects, without pausing to wonder whether they actually add much to the educational experience.

3. A module format offers many possibilities for cross-linking and internal referencing. But these can be too distracting. The number of cross links should be few if people are to maintain their focus and follow a coherent thread.

4. Similarly, the Internet offers endless possibilities for including additional material. But, again, the number of external links should be kept to a minimum if students are to focus on the content. Caution is needed when encouraging students to learn in a media-rich environment (22).

5. The module should be largely self-contained in terms of teaching material.

6. A final point concerns updating or correcting the material and exercises. It was advantageous that a system of normal HTML pages from an XML source was developed. Using this approach, especially when working with collaborators, makes it easier to correct errors and misunderstandings and update text and graphic images. Future compatibility is less clear; however, this uncertainty applies to the development of any e-learning system with a modicum of sophistication.

Lessons Learned During initial discussions, development, and redesign following feedback, we gained useful, valuable insights, particularly in view of the need for advice about effective, time-efficient ways to support student learning (10). We have distilled these six key insights.

1. E-learning requires a different approach from both teacher and student if any added value is to be achieved from the interaction with a personal computer. Teachers should be an integral part of the module production team. Students cannot be passive with an e-learning approach: it requires a high degree of individual motivation.

Figure 5. Screenshot, Remote Sensing Procedures, showing a summary of scores obtained working with a group of exercises.


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Conclusions

Literature Cited

The AT2 e-learning module, Remote Sensing of the Troposphere from Space, was devised and constructed to facilitate teaching of this subject to research students at the graduate level. The module could be regarded as an online textbook with these substantial advantages:

1. Martin, R. V.; Chance, K.; Jacob, D. J.; Kurosu, T. P.; Spurr, R. J. D.; Buc-

i. The module provides a straightforward and interesting introduction to a complex subject while still providing in-depth information on the topics. ii. The animations, such as those for the retrieval processes or scanning sequences of a satellite, are much more instructive than would be possible with a textbook. iii. The integrated, interactive exercises and reviews offer direct and immediate feedback to students about their understanding and comprehension of the material being studied.

However, we would emphasize that e-learning in this form is not intended to replace written material; rather it is a complement alongside traditional textbooks, lectures, and tutorials. A further important point regards open access to the module. Students with Internet access from all over the world can log in and use it to gain knowledge on the topic at the level in which they are interested. Such an approach facilitates learning globally and also helps encourage aspiring academics in the developing world to consider this promising field. In summary:

2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

• The module presents high-level material and allows students to test their understanding and obtain immediate feedback to improve their comprehension. (Students score their own performance.)

• The scientific content is presented as a series of nearly 100 illustrated and annotated study pages.

• Comprehension is tested by means of six different exercise types with a number of variants.

• The module is intended as an e-learning system, rather than a testing system.

18. 19.

• The module attempts to lead students through the processes of content assimilation.

20.

• The system is readily accessible online; the module uses standard HTML and an Internet browser.

21. 22.

• The module can run from a Web server, a file system, or portable media such as a CD-ROM or memory stick.

• The module can stand alone and is accessible from the Internet; it can also be implemented within most course management systems.

Acknowledgments The authors are grateful to AT2 colleagues for many initial suggestions and for module-testing feedback. We also thank the students and senior colleagues who tested the module at the June 2006 Heraklion feedback workshop. For encouragement throughout the project we also thank Evi Schuepbach of the University of Bern and coordinator of the ACCENT T&E project. The project was supported with funds from the EU through the ACCENT Network of Excellence. 756

15. 16. 17.

sela, E.; Gleason, J. F.; Palmer, P. I.; Bey, I.; Fiore, A. M.; Li, Q.; Yantosca R. M.; Koelemeijer R. B. J. Geophys. Res. 2002, 107, 4437–4456. Tropospheric Sounding from Space, Burrows, J. P., Borrell, P., eds.; AT2 in 2004-5, ACCENT Secretariat Urbino, 2005, Rep. 6.05; p 332. Schuepbach, E.; Challenges in Training and Education 2005: Position Paper. ACCENT Web Platform: http://www.accent-network.org/ (accessed Mar 2009). Wayne, R. Chemistry of Atmospheres, 3rd ed.; Oxford University Press: New York, 2000. Leue, C., Wenig, M.; Wagner, T.; Klimm, O.; Platt, U.; Jahne, B. J. Geophys. Res. 2001, 106, 5493–5505. Richter, A.; Burrows, J. P. Adv. Space Res. 2002, 11, 1673–1683. Richter, A.; Burrows, J. P.; Nüß, H.; Granier, C.; Niemeier, U. Nature, 2005, 437, 129–132. Home Page of the AT2 E-Learning Module on the Remote Sensing of Tropospheric Nitrogen Dioxide from Space. http://www.iup.uni-bremen. de/E-Learning/at2-els_NO2/index.htm (accessed Mar 2009). Friesen, N. Interactive Learning Environments 2001, 9, 219. Goodyear, P. Austral. J. Educ. Technol. 2005, 21, 82–101. Schuepbach, E.; Guggenbuehl, U.; Krehl, C.; Siegenthaler, H.; Kaufmann-Hayoz, R. Didaktischer Leitfaden für E-Learning; HEP Verlag: Bern, Switzerland, 2002. Law, R. J. Home Page of the LexEOS Exercise Builder. http://www. lexeos.com/ (accessed Mar 2009). Ladstätter-Weißenmayer, A.; Meyer-Arnek, J.; Richter, A.; Wittrock, F.; Burrows, J. P. Atmos. Chem. and Phys. Discuss. 2005, 5, 3105–3130. Meyer-Arnek, J.; Ladstätter-Weißenmayer, A.; Richter, A.; Wittrock, F.; Burrows, J. P. Faraday Discussion 2005, 130, 387. Burrows, J. P. J. Atm. Sciences 1999, 56, 151–175. Bovensmann, H.; Burrows, J. P.; Buchwitz, M.; Frerick, J.; Noël, S.; Rozanov, V. V.; Chance, K. V.; Goede, A. H. P. J. Atmos. Sci. 1999, 56 (2), 127–150. Gottwald, M.; Bovensmann, H.; Lichtenberg, G.; Noel, S.; von Bargen, A.; Slijkhuis, S.; Piters, A.; Hoogeveen, R.; von Savigny, C.; Buchwitz, M.; Kokhanovsky, A.; Richter, A.; Rozanov, A.; Holzer-Popp, T.; Bramstedt, K.; Lambert, J.-C.; Skupin, J.; Wittrock, F.; Schrijver, H.; Burrows, J. P. Monitoring the Changing Earth’s Atmosphere; DLR: Oberpfaffenhoffen, Germany, 2006. Platt, U. Chem. Anal. Series 1994, 127, 27–83. Solomon, S.; Schmeltekopf, A. L.; Sanders, R. W. J. Geophys. Res. 1987, 92, 8311–8319. Rozanov, V.; Diebel, D.; Spurr, R. J. D.; Burrows, J. P. J. Geophys. Res. 1997, 102 (D14), 16683–16695. Martin R.; Burrows J. P. IGACtivities Newsletter 2007, 35, 2–7. Guerin, H.; Watts, N.; Dervan, P.; Bury, G. E-learning Action Research Report, University College Dublin: Dublin, 2005. This ELearning! Magazine Web site has additional information about the report: http:// www.b2bmediaco.com/elearning/issues/summer07/summer07_featuredstory_3.html (accessed Mar 2009).

Supporting JCE Online Material

http://www.jce.divched.org/Journal/Issues/2009/Jun/abs750.html Abstract and keywords Full text (PDF) and links to cited URLs Supplement More details on the functionality and application of the six exercise types used to test students’ comprehension of the module

Discussion of potential advantages and uses of exercise types

JCE Cover for June 2009 This article is featured on the cover of this issue. See p 659 of the table of contents for a detailed description of the cover.


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