1.0 Introduction

The purpose of the Earth Observatory is to provide a freely-accessible forum on the Internet where the public can access new NASA satellite images and scientific information concerning our planet. As such, the site is intended to operate much like a popular weekly science news magazine; albeit published on the Web. Our focus is on Earth's ongoing climatic and environmental changes. The objective is to provide ample written and audio-visual resources that tell (and show!) stories concerning the causes and effects of change on Earth. The Earth Observatory is designed to take advantage of new, rapidly emerging Internet technologies in ways that "let the public in on the fun of Earth science." In particular, we hope our site is useful to public media and educators-any and all materials published on our site are freely available for re-publication or re-use. We ask in return that NASA's Earth Observatory be given credit for its original materials.

The purpose of this Style Guide is to assist editors, authors and computer graphic artists in preparing information for publication on this site. Here, all contributing authors and data visualizers are given credit for their original work. By submitting materials for publication in NASA's Earth Observatory, all contributors understand that their work is being placed in the public domain where it may be re-published elsewhere.

To both enable visitors to easily navigate the site, as well as to give us developers a way to "obviously" group types of information, the Earth Observatory uses a room metaphor interface. Each of the six rooms has a specific purpose and, therefore, each has a specific style. The following sections briefly describe the contents and function within each room. (Or, jump ahead to the Earth Observatory Style Guidelines section.)

1.1 Observation Deck

Among all the rooms, the Observation Deck is probably the most important as it demonstrates the unique perspective satellites can provide on global-scale, long-term changes. Global data sets of the key parameters (measured by NASA's Earth Observing System sensors) that drive climate change are available here. We group these data sets into categories: atmosphere, land, life, ocean, and energy. The global images in the Observation Deck are available as monthly averages, updated every month on an ongoing basis, at 1-degree resolution. We provide brief descriptions of each global data set, written in lay terms.

Visitors have the option of displaying these global images as either 2-dimensional movies, 2-dimensional "objects" that enable manipulation along two different time axes, or as static 3-dimensional spheres that visitors can rotate and zoom in on. (We selected Apple's QuickTime Virtual Reality as our format for presenting these global images. You may download a free QTVR viewer here.) Moreover, in the Observation Deck, visitors can visually correlate any two parameters, for any two time periods, in any of three aforementioned display options.

1.2 Study

The Study will contain science feature stories that describe new science results from NASA's Earth Observing System satellite missions and field campaigns. The text of these "case studies" will be complemented by local and regional satellite images (generally much higher resolution images than presented in the Observation Deck), as well as cartoon graphics and/or anecdotal photographs that illustrate and explain key concepts. In short, the purpose of the Study is to present a series of case studies that take the visitor to the frontiers of Earth science-placing emphasis on what we recently learned, what we still don't know, and how and why NASA scientists are studying a particular parameter or phenomenon.

Text and captions within the Study are written for the general public. Authors should emulate the styles of Discover, Popular Science, or Washington Post Science section articles when writing for this room. Text in the Study follows the guidelines detailed in the Chicago Manual of Style. Citations follow the style adopted by the American Meteorological Society.

1.3 Newsroom

The Newsroom is the repository for NASA's Earth science press releases, which are available here as soon as they are released by NASA's Public Affairs Office for publication. We will also include relevant press releases published by affiliated universities and other government agencies. NASA press releases are written in the standard "inverted pyramid" style that journalists use. With respect to grammar, capitalizations, and punctuation, the Newsroom follows the Associated Press Stylebook. The primary purpose of this room is to serve as a resource for public media.

NASA satellite imagery concerning significant Earth events (e.g., floods, volcanic eruptions, fires, and severe storms) will be published in this room in near real time. The Newsroom will also contain brief summaries of stories that are relevant to global climatic and environmental change that are currently being reported in the mainstream news media.

1.4 Library

The Library serves as the reference resource for the Earth Observatory. As such, it contains NASA Fact Sheets and other similar resources that contain background information on the terms and concepts presented throughout the site. The purpose of the Library is to serve as a research tool for anyone wishing to learn the basics on abstract Earth science topics, such as "What is El Nino?" or "What is a greenhouse gas?" The Library also contains a detailed glossary of terms and acronyms. The goal of this room is to place NASA's Earth science mission elements, scientists, data products, and new results into proper scientific context for visitors.

Text in the Library follows the guidelines detailed in the Chicago Manual of Style. Citations follow the style adopted by the American Meteorological Society.

1.5 Mission Control

As its name suggests, the Mission Control room enables visitors to track certain NASA satellites that are in orbit. Specifically, visitors can determine the location of a given satellite, as well as determine where on Earth a particular satellite sensor is gathering data.

1.6 Laboratory

Many people, children in particular, prefer to learn via "hands-on" exploration. The Laboratory provides interactive Web tools that visitors can manipulate to learn about the art and science of remote sensing, as well as the basics about the cause-and-effect relationships among the processes and parameters that NASA Earth scientists are studying. In this room, we will develop learning tools and activities that are targeted for specific age groups. As such, the purpose of the Laboratory is to facilitate the use of NASA satellite data and computer models in the classroom.

2.0 Earth Observatory Writing Style Guide

It is essential for science writers to know their audience and what information their readers need to understand their topic. The target audience for NASA's Earth Observatory is the general public. Yet, surveys show that even scientists who are reading about scientific subjects outside their area(s) of expertise prefer to read text that is written in a popular format. Therefore, authors contributing to this site should strive to write at roughly an 8th grade level of understanding. Section 2.1 presents the rules for writing for the Earth Observatory, while the following sections present some strategies and rules of thumb for effectively writing about science for the general public. (Or, jump ahead to the Rules for Citations section.)

2.1 Writing Rules and Guidelines

With the exception of the Newsroom, the Earth Observatory uses the Chicago Manual of Style, 14th ed. (1993), for general stylistic questions regarding proper English use-with respect to grammar, punctuation, capitalization, and vocabulary. The Newsroom follows the Associated Press Stylebook. The Earth Observatory authority for spelling and word definitions is Merriam Webster's Collegiate Dictionary, 10th ed. (1993). For the most part, the Earth Observatory follows the same standards adopted by the American Meteorological Society. The subsections below list the specific rules most likely of concern to prospective authors.

1. Capitalizations

Proper names of locations and phenomena are capitalized-North Carolina, Mississippi River, Sahara Desert, Southern Hemisphere, the Tropics, the Gulf Stream, and El Nino are all written correctly.
2. Units

As does the American Meteorological Society, the Earth Observatory uses the International System of Units [Systeme Internationale (SI)] for units of measure as well as chemical elements. Temperature, for instance, is given in either kelvins (K) or degrees Celsius (�C).
3. Numbers

Spell out numbers zero through nine, and write as numerals numbers 10 or greater; except when a sentence includes two numbers in the same context that are both above and below nine. In this case, write "4 out of 10 samples" rather than "four out of 10 samples." Also spell out numbers that begin a sentence.
4. Date and Time

Write the day, month, and year in the form "12 March 1999" in the Earth Observatory. Do not abbreviate months. The recommended time zone annotation system is universal time, abbreviated UTC. Write the time, time zone, day, month, and year in the form "1421 UTC 12 March 1999." Alternatively, you may use other time zones, such as EST, EDT, PST, or LST (local standard time), but you must define the standard you use on your first use. For year ranges, do not include the century in the second year unless you describe a transition across centuries. For instance, "1982-99" and "1897-1999" are correct uses.
5. Latitude and Longitude

Latitude and longitude pairs should be expressed in that order; for instance 37EN, 182EW. For locations along the equator, the Greenwich meridian, or 180E longitude, omit the hemisphere letter-"0E, 152EE"; "32ES, 0E"; or "56EN, 180E" are correct.
6. Monetary Values

Convert all monetary values to American dollars. Place the dollar sign ("$") before the number-"$450,000." Write out values greater than a million-"$450 million" or "$1 billion."

2.2 Strategies for Writing Effectively About Science

2.2.1 Active vs. passive voice

Writing in the passive voice generally focuses the reader on abstract concepts; however, our objective is to render our subject matter less abstract. Our goal is to focus on people who do things . Therefore, authors should use active voice throughout the Earth Observatory.

When we write in the passive voice, we do four things:

1. We either delete the original subject, or put it at the end of the sentence with "by" before it;

2. We transfer the direct object to the subject slot;

3. We substitute the past participle of the verb in the verb slot;

4. We add a form of the verb "be" as auxiliary to the past participle.

Consider the following sentence, written in passive voice:

The Theory of Relativity was written by Albert Einstein.

Consider the same sentence written in the active voice (although the verb is past tense, which differs from passive voice):

Albert Einstein wrote the Theory of Relativity.

2.2.2 Nominalizations

Turning a verb into a noun is called a nominalization. (The term "nominalization" itself is a nominalization.) We nominalize verbs and adjectives by adding "y," "tion," or other such constructs, so that "discover" becomes "discovery," "investigate" becomes "investigation," "apply" becomes "application," and so on. Be judicious in their use because nominalizations both contribute to and are a symptom of the use of passive voice. Don't write: "A discovery was made when the investigation was conducted in which the application of chemical x onto substance y was found to cause symptom z." Instead, write: "Jane Doe investigated chemical x. She applied chemical x to substance y and discovered that it causes symptom z."

2.2.3 Jargon and Acronyms

Each science discipline has its own particular jargon-scientists discover new things and must sometimes invent new words that describe those things. You can typically spot jargon terms in the form of noun strings, which scientists often condense into acronyms. However, when writing for the Earth Observatory, authors should avoid the use of scientific jargon. If it is necessary to include a jargon term, then be sure to include a simple definition of the term. Or, consider ways to reword the term to make its meaning more obvious, possibly by adding hyphens to group words or by adding one or more prepositions to emphasize unstated relationships. For instance, "low cost fuel handling and storage systems" could be rewritten "low-cost systems for handling and storing fuel."

Avoid using acronyms. Use them only when their meaning is common knowledge, such as "NASA." Or, use them only when writing an article that requires frequent use of a noun string. Once you have told your reader what a "Normalized Difference Vegetation Index" is, you can subsequently refer to it as "NDVI."

2.2.4 Vague Pronouns

Avoid using vague pronouns (e.g., it, they, that, this, something, one), especially at the beginning of a sentence. It (science) can be hard enough to understand, without them (readers) having to guess what he (the author) meant by it (his text).

2.2.5 Sentence Structure

A common criticism of scientific texts is that their sentences are hard to understand because they are too long. However, "too long" does not mean too many words. A sentence is too long when its structure gets in the way of reader understanding. Writers sometimes compound structure problems in their sentences by interrupting the subjects and verbs with lengthy modifiers. Readers expect subjects to be followed closely by verbs. Readers regard any phrases that come between subject and verb as an interruption and, therefore, as having less importance than the information in the stress position of a sentence.

2.2.6 Figurative Language

Authors contributing to the Earth Observatory should do more than merely relay scientific or technical information-we should entertain the reader by weaving figurative language into our text. We should even strive to add a sense of drama, excitement, frustration, confusion, or humor when appropriate and relevant. The use of figurative language can serve to add a human element to text, while making a subject less abstract and more easily understandable to the reader. In particular, using analogy, metaphor, simile, and sometimes even personification (techniques typically found in poetry) can render abstract concepts more "alive" and vivid. Figurative language also introduces some redundancy, which is often good to do when communicating abstract concepts to the lay public. (The following subsections discuss the use of specific types of figurative language. Click here to jump ahead to the next section on Earth Observatory Audio-Visual Format Standards.)

3.0 Rules for Citations

The Earth Observatory uses the American Meteorological Society's style for citing other works. Citations in the text should consist of the author's name and year of publication, both within parentheses-for instance (Jones 1998). If there are three or more authors, state the first author's name, followed by "et al." and the year of publication. The format for compiling a works cited list is as follows:

For a journal or magazine-

Author(s), publication year: Article title. Journal name, volume, page range.

For a book-

Author(s), publication year: Book Title. Publisher, total pages.

4.0 Audio-visual Format Standards

To get the best results preparing images for the web (and the Earth Observatory), we use different compression techniques for varying types of images. Photographs are compressed most efficiently by JPEG set at 70 percent (medium to high quality). Images with large areas of flat color, well-defined edges (such as text), or small size (less than 100-by-100 pixels) should be compressed and saved as GIFs. Reducing the number of colors in a GIF can often provide additional compression with little loss in image quality.

To further improve performance on the web, we will use "HEIGHT" and "WIDTH" tags in images in the Earth Observatory. For images with large file sizes, we will also make available a low-resolution version, added to the "IMG" tag.

4.1 The Basics of Computer Images

Computers generally store and display images as an array of pixels. Grayscale (black and white) images use one byte (eight bits) per element in the array (picture element, or pixel) to represent brightness. This results in a range of 256 shades of gray that your monitor can display. (The human eye distinguishes between 30 and 40 levels of gray.) True color images combine three 8-bit grayscale channels-red, green, and blue-per pixel to represent 16.7 million shades. This is the "RGB" color space, which roughly matches the limits of human perception.

Subsets of the RGB color gamut are often used to reduce memory, storage, and performance requirements for working with computer graphics. Entries in a color table (palette) assigned to individual colors in the full RGB gamut are one method for subsetting. Eight bits are commonly used for each address in the color table, which results in the display of 256 colors, but other values are also used (1 bit is common). Several different methods may be used to convert 24 bit images to indexed color. These colors are sometimes predefined (as in the Windows and Macintosh system palettes) or they can be generated based on the hues present in the original image. Images that originally had a wide range of colors suffer from "banding"-strips of solid color where smooth gradations originally existed. "Dithering" is used to reduce this effect. Subtle variations of color are reproduced by similar colors placed side-by-side. For example, a medium blue could be simulated by sky-blue and navy pixels next to each other. These dithering patterns can be regular (preferable for even gradients), or irregular (preferable for natural images).

Indexed color palettes also provide a good way of displaying single parameters of scientific data.

Sixteen-bit color (thousands of colors) is another method of subsetting images. Five bits per channel are used instead of eight. This is often combined with dithering to simulate the full RGB gamut.

4.2 Preparing Images for the Earth Observatory

High quality source imagery and appropriate compression techniques will result in the best possible graphics for the Earth Observatory. Photographs should be at the resolution at which they will be used, or higher, and have brightness and contrast appropriate for display on Macintoshes, PCs, and UNIX workstations. Ideally they should either be uncompressed, or compressed by a "lossless" method. The quality of JPEGs initially at high quality settings degrade minimally when recompressed so they are also acceptable. Photographs that have been dithered are generally unacceptable. It is often a good idea to crop photographs to the area of interest. Graphics (line drawings, plots, and diagrams) and text should be anti-aliased and it is essential that they are not dithered.

Photographs and photograph-like images should be saved as JPEGs to optimize quality and maximize the reduction in file size. Compression level should be set to "medium high" quality, roughly 70 percent. Photographs with very high sharpness and contrast and/or smooth gradients usually benefit from higher quality settings, while very "natural" images can be compressed more with little loss in image quality. JPEG compression is lossy, so recompression should be avoided, and it is advisable to save a copy of the original (uncompressed) artwork.

Graphics, rasterized text, and other images with sharp borders and flat color should be saved as GIFs. Monochrome graphics generally look good as 3-bit undithered images. As a rule of thumb, add 1 bit per extra color-a 2-color graphic probably requires 4 bits, or only 16 colors!

Small images such as thumbnails, should also be saved as GIFs. Because they have fewer pixels, they do not suffer significant degradation when converted to indexed color. Undithered 6-bit images look surprisingly good, but complex images may require higher bit depths.

Compression methods and file types for images generated from scientific data also vary. Color composites are essentially photographs, and should be treated as such. Images from data using a maximum 8-bit color palette can be saved as GIFs without any loss of information, so even though they may be larger than a comparable quality JPEG, it is useful to save them as GIFs. If the image has been resized, however, the interpolation of pixels changes their value anyway, so JPEG will provide better image quality at a lower file size.