CoastWatch CoastWatch West Coast Regional Node
Home | CWBrowser | Sites | Feedback

CWBrowser
The CoastWatch Browser

Description | How do I ... | Details | GET Queries | Grid Data File Types | Station Data File Types | FAQ | Credits | Disclaimers | Contact

Description

CWBrowser is an interactive web page for selecting, viewing, and downloading oceanographic data (satellite and in-situ, near-real-time and science quality) for the west coast of the U.S. and Mexico. It creates custom maps on-the-fly of the data that you select. The maps can include colored surfaces (coverages), contour lines, markers, and vectors from different datasets. The data can be downloaded in several different grid data file formats and station data file formats.

Environmental Data vs. Weather Data - CWBrowser deals with environmental data (for example, sea surface temperature, ocean winds, chlorophyll levels). If you are looking for weather or marine forecasts, please go to the NOAA National Weather Service.

West Coast of U.S. and Mexico vs. Other Regions - This version of CWBrowser only deals with data for the west coast of the U.S. and Mexico. For other data sets and other regions, please visit

Brought to you by ... CWBrowser is part of (and was created by) the West Coast Region Node of the CoastWatch Program,
which is part of the National Environmental Satellite, Data, and Information Service,
which is part of the National Oceanic and Atmospheric Administration (NOAA),
which is part of the U.S. Department of Commerce.

 


How do I ...

Are you new to the program? Here are a few recipes for common uses of the program.

 
How do I specify the geographic region that I am interested in?

 
How do I view and then download satellite data?

 
How do I view and then download satellite time series data?

 
How do I view and then download satellite vector (e.g., wind) data?

 
How do I view and then download station data?

 
How do I view and then download station time series data?

 


How do I use the program (the details)?

The green Edit row lets you specify which part of the map you want to edit.

Edit: The Map - has options related to the entire map. The options are:

Edit: Grid Data - lets you specify the gridded data which will be drawn as a colored surface on the map. Areas which are invalid (because of clouds, or land, or because the satellite did not pass over that location) are gray. The options are:

Edit: Contour Data - lets you specify if contour lines for other data should be drawn on the map. Note that contouring only works well if the data has large contiguous areas of valid data. If you don't see the contour lines you expected to see, map the data as the Grid Data and verify that there are large contiguous areas of valid data. The options on the Edit: Contour Data screen are:

Edit: Vector Data - lets you specify if vectors for other data (e.g., wind) should be drawn on the map. Note that vectors are only drawn at a few of the points for which data is available. A given vector represents the data for the location at the base of the vector. The options are:

Edit: Station Vector Data - lets you specify the station vector data which will be drawn on the map. The options are:

Edit: Station Data 1/2 - lets you specify the station data sets which will be drawn on the map. You can plot and compare up to 2 station data sets. The options are:

 


GET Queries

It addition to CWBrowser's graphical user interface, CWBrowser lets you download data files without using a graphical user interface, via HTTP GET queries. For example, you can download GOES SST gridded data (which has an internal name of "LGAssta"), from 2006-04-11T00:00:00, for longitude 135°W to 115°W, for latitude 22°N to 50°N, as an .nc file with the url?query: CWBrowser.jsp?get=gridData&dataSet=LGAssta&timePeriod=1day&centeredTime=2006-10-24T12:00:00&minLon=-135&maxLon=-105&minLat=22&maxLat=50&fileType=.nc .

This system's intended end user is a computer program or a script which downloads some data from this server. Thus the communications are intended to be computer-friendly. If you want a people-friendly graphical user interface, use CWBrowser's graphical user interface.

This system uses a Distributed Access Protocol (DAP), analogous to OPeNDAP. Unlike OPeNDAP, in which you specify the data you want by specifying index ranges for data arrays, this system lets you specify the data you want based on actual longitude, latitude, and time values. Thus, this system is sort of a space-aware and time-aware alternative to OPeNDAP.

For details of how to form the queries, just start using the system with the start of a query: CWBrowser.jsp?get . The system's error messages will help you add other parts of a query. When you have a complete query, the data file will be download to your computer.

 


Grid Data File Types

If you select Edit: Grid Data, Edit: Contour Data, or Edit: Vector Data, you will see links to download the gridded data that you have selected. Grid data can also be downloaded using GET Queries. All of the grid file formats are available via GET Queries, but a few of the options are not listed on the GUI web page. The available grid file formats are:

OPeNDAP - If the current data set is downloaded on-the-fly from an OPeNDAP server, CWBrowser displays this link so that you can use OPeNDAP to access the data from its source.

SeaWiFS chlorophyll-a data less than five years old is not available for downloading because of the terms of the contract NOAA has with GeoEye, the company that owns the private satellite which is the source of that data. Under some circumstances, we can make this data available. For more information, please contact dave.foley@noaa.gov.

Grid Vector Data Files (available from the Edit : Vector Data : Download the vector data) are very similar to grid data files. The only difference is that the files include two data grids (the u and the v data components) instead of one. Grid vector data files are available in these formats:

ArcGIS is a family of GIS products from ESRI. You can buy different levels of ArcGIS: ArcView (least expensive, least capabilities), ArcEditor(mid-range), and ArcInfo(most expensive, most capabilities). All levels of ArcGIS include the ArcCatalog and ArcMap tools, and both of those contain a lower level tool called ArcToolbox. ArcGIS can import grid data from GeoTIFF and ESRI .asc files.

For GeoTIFF files: When ArcMap initializes there will be a table of contents on the left and a map window on the right. Click the + icon to add data to your data frame. The Add Data dialogue box pops up. Navigate to and select a GeoTIFF. Click Add. The image should display in the map window. By right clicking the file name in the table of contents, and selecting Properties, the user can adjust the stretch, apply color ramps and conduct additional modifications.

For ESRI .asc files:

Shapefiles - We do not distribute grid data as shapefiles because shapefiles are usually an inappropriate file format for distributing grid data. If the grid data is stored in a shapefile, it is either treated as sets of points (MultiPointM or MultiPoint objects, where one loses the information that the points are arranged in a grid) or as a Polygons (where one deals with contiguous areas with a specific range of values, for example, 16 degrees <= Temperature < 17 degrees, where one loses the actual data values and the information that the points are arranged in a grid). Such shapefiles can and should be derived from the original grid data, which we do distribute.

We believe that the ESRI .asc files available from CWBrowser are the appropriate form for distributing grid data to the ArcGIS programs. In fact, this ESRI .asc format was designed by ESRI for this exact purpose -- the transfer of grid data between computers.

 


Station Data File Types

If you select Edit: Station Vector and Edit: Station Data 1/2, you will see links to download the station data that you have selected. If you select Edit: Grid and click on the map, you will see links to download the time series created from one point from a time series of lat lon grids. Station data can also be downloaded using GET Queries.

The supported station data file types are:

The columns in the station data files are always:

 


Frequently Asked Questions

How does the program work? The goal of this program is to help you quickly select data from among the data that is actually available. On the CWBrowser web page, a large number of options are available via one small, somewhat unusual (but hopefully easy-to-use) HTML form. Each time you make a selection in CWBrowser, a "Please wait" message will be briefly displayed. Then the web page will be refreshed with new options lower on the HTML form. This allows CWBrowser to show you just valid options. For example, on the "Edit : Grid Data" screen, if you select a different data set, the time period options will change so that you just see valid options for that data set. If you then select a different Time Period, the Centered Times will change so that you just see valid options for that data set and that time period. (See "Why is the program set up this way?" below.)

Why is the program set up this way? The data sets are so varied that this is the best approach. Some other data-selection programs make you submit search requests to a database; the searches often result in either too many matches (how do you choose the best?) or zero matches (now what do you do?). Some other data-selection programs take a similar approach to CWBrowser but spread the options over several web pages, making it awkward to make changes and leading to frustration when the results at the end of a long process aren't what you had hoped for. CWBrowser always shows you a map with the currently selected data. We admit that our approach is biased toward users (like scientists) with fast Internet connections.

Why is there no Submit or Go button? Because the form on the web page is set up to automatically submit every choice that you make as soon as you make it, there is no need for a Submit or Go button. A minor exception is TextFields: press Enter to submit the information when you are finished editing the text. Note that if you have disabled JavaScript in your browser, a Submit button will appear on the web page.

Why did the program forget my previous selections? If you don't use the program for 30 or more minutes, your session times out and information about your previous selections is discarded. In some situations, the first use after a period of inactivity can lead to an error message. We're sorry that this can occur, but we can't keep information about users' selections forever. 30 minutes is a typical, and hopefully reasonable, time out period.

Why is the map so small? The standard .png image of the map is designed to fit on the screen along with all of the controls so that you can interactively manipulate the map. At any time, you can view a larger image by choosing Edit: Map and then Select a size: Large. If you want a smaller map (because you have a smaller screen or a slower internet connection), you can get one with Select a size: Small. Note that if you download the .pdf version of the map, its size is also affected by the Select a size setting.

Near-Real-Time Data vs. Science Quality Data - Near-real-time data is data that is between a few minutes and a few months old. The goal is to make the data available as soon as possible. Science quality data is data which is at least two months old. The extra time is used for additional quality control and validation of the data. Sometimes different processing methods are used for science quality and near-real-time data sets.

CWBrowser has both near-real-time and science quality data sets. Near-real-time datasets may or may not be labeled as such. Science quality data sets are always labeled "Science Quality".

Why don't the colorbar's min and max values change based on the data values?
Why is the colorbar's min and max tied to the data set and not the actual min and max of the data on the current map? Answer: because changing the values based each image's data would make it difficult to compare maps that should be easy to compare. For example, if you are clicking on the + or - button for Select a centered time, it is hard to compare successive images if the colorbar's min and max values change. Similarly, if you are viewing different regions (e.g., Seattle vs. San Diego), it is hard to compare the maps if the colorbar's min and max values change. If you want to change the colorbar's min and max, it is easy to do. The current range is visible where you would go to change it (Edit : Grid Data then Select a palette: Min or Max) and also on the image (at the top and bottom of the colorbar).

Why is there so much missing data? For most types of measurements, clouds cause inaccurate readings. So cloud contaminated data is removed. Since many of the satellites are not geo-stationary, other gaps are caused by limited satellite coverage.

Why do I see diamond-shaped holes in the data? For composite time periods, each colored square on the map (representing a tiny region of the ocean) represents the mean of the valid (i.e., non-cloud) readings for that region taken during that time period. The POES (polar orbiting) satellies take readings in diagonal swaths as they move from near the south pole to near the north pole (or vice versa). There is a gap between measurements from ascending (or descending) swaths. The union of the gaps between ascending swaths and descending swatchs often forms a diamond shape. For composite data from more than 1 day, there is usually enough data to fill in these gaps.

Why do I see cloud-like patterns on the map?
Why do I see what appear to be temperature fronts that are diagonal lines? For composite time periods, each colored square on the map (representing a tiny region of the ocean) represents the mean of the valid (i.e., non-cloud) readings for that region taken during that time period. Because the number of valid values varies for the different pixels, the map is inherently imperfect. Even though cloud contaminated data is removed, you may see cloud-like patterns. Consider a composite made up of two satellite passes. For the first pass, the temperatures are generally cooler and there are scattered clouds. For the second pass, the temperatures are generally warmer and there are no clouds. When the two passes get averaged, pixels with one valid value (from the second pass) will tend to be warmer than pixels with two valid values (the mean of the warmer and the cooler passes). As a result, you see cloud-like patterns made up of one-valid-value pixels.

The same type of thing happens at the edges of satellite passes, causing what appear to be temperature fronts that are straight diagonal lines (colder on one side of the dividing line and warmer on the other).

With composites of longer time-periods, these effects are minimized.

There is another possible problem: while we try our best to provide the best possible data, there is no way to be sure we accurately identify and mask every cloud. The cloud mask we now use is the best we have found, but it is quite conservative (that is, it is more likely to see clouds where there are no clouds than it is to not see a cloud where there is a cloud): but there is still cloud contamination, generally due to low stratus clouds. If you want us to check out a specific image or for details concerning the cloud mask we use, please contact dave.foley@noaa.gov.

 


Credits

 


Disclaimers

DISCLAIMER OF ENDORSEMENT
Any reference obtained from this server to a specific commercial product, process, or service does not
constitute or imply an endorsement by CoastWatch, NOAA, or the United States Government of the product,
process, or service, or its producer or provider. The views and opinions expressed in any referenced
document do not necessarily state or reflect those of CoastWatch, ERD, NOAA, or the United States
Government.

DISCLAIMER FOR EXTERNAL LINKS
The appearance of external links on this World Wide Web site does not constitute endorsement by the
Department of Commerce/National Oceanic and Atmospheric Administration of external Web sites or the
information, products or services contained therein. For other than authorized activities, the Department
of Commerce/NOAA does not exercise any editorial control over the information you may find at these
locations. These links are provided consistent with the stated purpose of this Department of
Commerce/NOAA Web site.

DISCLAIMER OF LIABILITY
Neither the data providers, ERD, CoastWatch, NOAA, nor the United States Government, nor any of their
employees or contractors, makes any warranty, express or implied, including warranties of
merchantability and fitness for a particular purpose, or assumes any legal liability for the accuracy,
completeness, or usefulness, of any information at this site.

USAGE LIMITATIONS
The SeaWiFS images and data from this site may be used for free, but not redistributed;
all other images and data from this site may be used and redistributed for free.

 


Contact

Please email questions, comments, or suggestions regarding this web page to dave.foley@noaa.gov. We would really appreciate knowing if you use the CoastWatch Browser.

 


Privacy Policy USDOC | NOAA | NESDIS | CoastWatch | West Coast CoastWatch