How do I download data from WISE?

From CoolWiki
Jump to navigationJump to search

General Information and/or Links of Interest

WISE EPO tutorial on downloading data from Berkeley - generic, for the general public. May be slightly out of date.

Explanatory Supplement for WISE all-sky release - the document that explains everything about everything in the WISE release, aimed at professional astronomers.

Tutorial videos from IRSA for WISE data - again, aimed at professional astronomers.

Inaugural NITARP Tutorial: Part 1: WISE overview - what is the mission, the big picture (20 min); Part 2: the WISE archive - how to access the archive (20 min); Part 3: questions - questions from those online and on the phone (8 min)

Accessing the WISE Archive

There are two main ways to access the WISE data. One is via a web-based user interface that provides easy access to both images and catalogs from WISE, as well as other places on the internet. It looks a lot like the Spitzer Heritage Archive, the Planck Archive, and others to come. The other, called Gator is a somewhat simpler web-based interface to just the catalogs, from WISE and many other archives. (Technically, there are also other ways to access the WISE data, such as via computer code, but we won't go into that here.) It's probably simplest to access it via the web-based user interface, so that is what we will cover (briefly) here.

For all of these web-based user interfaces that look like this, if you let your mouse hover over things in the window, you often get a "tool tip" that pops up to help explain more about what you are looking at. There is also often context-sensitive help -- look for little blue circled question marks, and click on them to get more information about whatever it is. You can also access the online help directly from the "help" menus near the top of your window. (NB: If you go to "education and public outreach", you'll get dumped into the NITARP website, as opposed to find out more information about that specific archive.)

Searching for images by position

When you first go to the WISE archive, you're dropped right away into a position search. That's the most common way for people to search the archive. There are other options, and you should feel free to explore them, but we won't cover them here.

By default, you're dropped into a single object search. (You can also search for multiple positions at once; see the online help for instructions on the file format.) Type in the name or position of the object you want. Note that it echos what it thinks you've typed right below the entry window. If you are using a very common name, NED or Simbad can resolve the name; if not, you will need to enter coordinates. For this example, let's use "BRC 27". Neither NED nor Simbad knows what this is, so we need to type in coordinates. Use 07:03:59 -11:23:09.

The rest of the options on the main search screen are ok to leave as defaults. We want the image to contain the target we are searching on (as opposed to the other options on that pulldown menu). The image size of 600 arcseconds is ok for now, though you may want to increase/decrease this as your needs dictate. You can also input the size in arcminutes or degrees -- change the pulldown to change the units. We want to only have the image most centered on the target. We want all four WISE bands to be returned. We want the Atlas images. Click "search" and off it goes.

Search results

When it returns, it has given you two big "window panes" and four smaller ones. At the top, it reminds you what kind of search you did ("position") and on what ("105.99583333333332;-11.385833333333332;EQ_J2000; Type=CENTER; Image Size=0.1667 deg; Product Level=3a; allsky-4band"). Right underneath that, on the left, it has three tabs within the top left window pane. The top is "Coverage", which shows you a visualization of the WISE tile on top of an IRAS image. The small blue circle near the top of the big square is the target position on which we searched. The next tab is "3 color", and this assembles a 3-color WISE image of our region. Again, the blue circle is the target on which we searched. The 3rd tab is "Details", and this includes a bunch of operational details about the observation.

The window pane on the top right summarizes for you what observations met your search criteria. For this search, there are 4 bands, with identical coadd ids, nearly identical dates of observation, and similar numbers of frames.

The four images along the bottom are all four of the WISE bands, with the sizes corresponding to the region on which we searched. Again, the blue circle is the target on which we searched.

For any of the images displayed (on the bottom or the top left), if you move your mouse over the image, you get a popup window at the top of the browser window telling you information about where your mouse is - RA, Dec, image value, etc. When your mouse is over an image, you also get some additional options in that image window. At the top right of the image window, you can click on the black arrows to expand that image to fill your full screen, or click on the tools to change some of the settings (like stretch and color table).

If you do a search on more than one region, or your search is large enough to encompass more than one WISE tile, your display will look a little different. To see this, go back and search again. Click on the "Searches" tab in the upper left. Leave the position as we did above, but for "search type", pick "Any pixel overlaps search region" and change the search region to 20 arcmin. Click on "search."

When it returns, you can see in the upper left that it has returned 3 tiles. On the right, it shows you 3 sets of 4 bands of images. The lines highlighted green are the ones whose images are at the bottom, and whose tile is blue on the left visualization. Click on one of the next set of WISE images, and see how things change.

Downloading images

To download images, go to the window pane in the upper right. Click on the checkboxes to the left of the row you want to download. If you want to get them all at once, click on the checkboxes on the top of that column. Then click on the "Prepare Download" button just above the checkboxes. It will give you a popup window asking what, exactly, you want. You want all four bands, possibly you want the ancillary files, and you can choose whether to have the files sorted by subdirectory or not. If you are asking for a lot of data to be downloaded, it may take a while to package, in which case you probably want to enter an email and have it tell you when it is done packaging. Click "prepare download" and off it goes, collapsing the window into a little link at the top right. If you click on that, you can watch it package. It will tell you updates about its status - "preparing" or "new job ready". When it is done, you can click on "download now" (or the links provided in the email it sends you) to download the data. To uncompress it, double-click on it, or type "unzip <filename>" from a terminal window.

Catalog searches

This interface also allows you to explore the catalogs delivered by the WISE team. Go back and do a simpler search like the first one above: search on 07:03:59 -11:23:09, tell it you want the image to contain the target we are searching on, and pick something 'reasonable' like 10 or 20 arcminutes for an image size. Click search.

When you are looking at the results page, go up to the top center, and pick the blue "Catalogs" tab. This interface provides you access to MANY catalogs. By default, it comes up as offering 2MASS. For this example, change it to WISE. Go to "Project" in the lower left of the white window, and change "2MASS" to "WISE". Note that several other things in the window change accordingly. The default "category" of "WISE All-Sky Database" is what you want (bottom left) and the default "All-Sky Source Catalog" (green bar, upper right) is what you want. The search method has automatically filled out for you a region corresponding to what you have requested in images. Click "search".

It most likely spins off into a background monitor job, just like the images above. When it is done, click on "show catalog" from the background monitor.

When you do that, it spawns another tab in the upper right window pane, this one corresponding to the search results of the catalog search. Note that it probably has several pages -- mine tells me "(1-50 of 1043)" near the top of the tab. This indicates that 1043 sources met my search criteria, but it is only displaying the first 50. To change this, click on the little blue box in the upper right of that window pane, and change the "page size" in the pop-up. Click OK to implement it. (This is also how you change what columns are displayed, if desired.)

Now, it has also overlaid the source list in the four WISE images at the bottom of the screen. The blue circle is still your search target; the red squares are every object out of the 50 shown in the tab, and the blue square corresponds to the row highlighted in green in the catalog tab. This is extremely useful if you are trying to identify a particular source in your image. Click on a row to see it called out in the image; click on the symbol in the image to get it called out in the catalog tab. If you have trouble distinguishing red and blue, click on the blue "plot layers" tab and change the colors it uses.

The various columns that are returned by the catalog search include the detection name, RA/Dec, and its profile fitted magnitudes in each band, plus errors. "w1mpro" is "profile fitted w1 magnitude". "w1sigmpro" is the uncertainty (sigma) on that measurement. Let your mouse hover over the columns to get a tooltip explanation of what it is. Go to the official release documents (linked at the top of this wiki page) to read all about what the number is, how they got it, when to not trust it, etc.

SEARCH CATALOGS WITH CAUTION. It is very easy to ask for thousands upon thousands of sources. I get 66,000 2MASS sources over a degree centered on BRC 27, and 32,000 WISE sources in that same region. If you ask it for this, it will take a LONG time to retrieve and display. Be sure that this is what you really want to do before you do it; conversely, if it's taking a very long time, maybe you didn't ask for as simple a request as you thought.

To save the catalog to disk, click on "save" at the top. It should save the whole thing, not just the 50 rows displayed. It save it as an IPAC table file, which has a ".tbl" extension. It is really a plain text file. Your computer might not know what to do with a *tbl file; if that is the case, just rename it to be a ".txt" file, and then you can open it using nearly anything. I recommend using something like Excel to open it, because you can import the columns in the text file into columns in an Excel spreadsheet. (YouTube video on what tbl files are, how to access them, and specifically how to import tbl files into xls -- 10min)