The pass selection interface allows you to search our database of all passes we have received since 1978. The search can be narrowed to a selection of satellites, between a range of dates, where specified locations are visible. A more complex search can be performed which allows you to find passes with a range of orbit numbers or archive tape identification numbers.

You can use the results of the search for ordering high resolution data or photographs, or simply for browsing thumbnail images for your area of interest.

Select locations graphically?

First choose whether you want to select locations graphically. You don't need to specify any locations but if you do then you can either type them in using latitude and longitude or select them by clicking on a map.

Complex query?

Second choose whether you want to make a complex query. This option allows you to test the cloud cover over a specific location, or limit the search to specific hours of the day. It also has many other option which are more useful for users with a detailed knowledge of the database.

Select locations

If you have chosen to select locations graphically a map will be visible. You should select one or two locations now before altering any other options. This is because clicking on the map resets the values for satellite / date / orbit / tape.

Choose scanners or satellites

The required scanners or satellites can now be chosen. You can select one, many or even all satellites, but typically you will simply select one scanner (AVHRR being the most common) which implies all satellites carrying that scanner. How you select multiple items depends on your browser -- some require the CTRL key to be held down, some allow you to drag a selection, others select multiple entries automatically.

Enter range of dates

Enter the start and end dates, ensuring that you use the European convention of writing the day before the month. For example, enter the 12th of February 1995 as 12/2/95.

An alternative range of dates can be specified using a number of hours before the present time. For example entering 48 hours will search for all passes received within the last two days. This parameter takes precedence over the explicit date ranges above. It can be useful because the same query can be used without modification in the future to select recent passes at that time. The URL can be bookmarked but for clarity you should delete the dates in the From (start=) and To (end=) fields.

Enter locations by coordinates

If you are not using the map you can enter one or two locations which must be visible. There is no requirement to enter any locations but if you do then they must be in the form <degrees> <direction> <degrees> <direction> where degrees is a number between 0 and 90, and direction is W or E, (for longitude), N or S (for latitude). The value of degrees should be an integer (ie. no fractional part). Both a longitude and a latitude must be present. For example, enter the location of Dundee (56 degrees North, 3 degrees West) as 56 N 3 W.

Multiple Locations

If you enter more then one location, either by coordinate or by the map, you can combine them using AND or OR. If you select AND then only those passes which contain both locations will be returned. Selecting OR will return all passes which contain one or other (or both) locations.

Enter other criteria

If you chose a complex query then you can enter orbit numbers, equator crossing angles, or tape numbers. Note that the angles should be given as positive integer degrees West and that the tape number should not contain the track number or side indication. Values can be entered as ranges, eg. 1200 - 1350. The start or end numbers of the range may be omitted, defaulting to zero or maximum respectively. AVHRR Channel 3 may be transmitted as visible or thermal on satellite NOAA-15 onwards. The search option VIS returns only passes where some part of the pass contains visible channel 3, but it is not guaranteed that it is the visible channel at your chosen location. Really this is more a way of ruling out thermal-only channel 3 passes for example. The cloud-mask option calculates the cloud cover over the first location chosen (at least one location must be selected). It is not perfect but is designed to allow you to rule out definitely cloudy scenes (scenes where the cloud cover is not certain are not marked as cloudy). The percentage is based on an accumulation of the cloud cover in the area surrounding the chosen location.

Results

The results of the search can be displayed graphically, using a small `thumbnail' image of each pass (where available), or as a simple textual list. As each thumbnail can be up to 20 kbytes you may wish to opt for a list first to save time. If you chose a complex query then the orbit and tape numbers and equator crossing angle will also be displayed. Thus you can find on which tape a particular pass resides.

Repeated searches for a particular location

If you often perform searches using the same coordinate(s) you can add a link to your browser's hotlist so that you don't have to click on the map each time. Just click once or twice and then add the current page to your hotlist. The URL will contain the elements /map/x0/y0/x1/y1 where the x and y values are the coordinates as clicked on the map.


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