NASA Worldview, New Interface

Mick West

Administrator
Staff member
https://earthdata.nasa.gov/labs/worldview/


Lovely update to NASA's Worldview page, which allows you to looks at MODIS images and other data overlays from any day in the last few years, anywhere in the world. They have replaced the "click a day" interface with a date slider. But the great things about it is that the images get cached locally, so once you have gone through a range of images, you can scrub back and forth, and see the large scale movement and development of weather systems. You can also use the arrow keys to do this.
 

WeedWhacker

Senior Member
once you have gone through a range of images, you can scrub back and forth, and see the large scale movement and development of weather systems. You can also use the arrow keys to do this.

This is really great, an asset to debunk so-called "chem"trails and so-called "spraying".

In past, using time-lapse videos taken from a fixed position on the Earth's surface was useful, but this gives a much "bigger picture", as it were.
 

Mick West

Administrator
Staff member
Only one photo per day, unfortunately. Although you can toggle between Terra and Aqua, which are about an hour or so apart.
 

WeedWhacker

Senior Member
Although you can toggle between Terra and Aqua, which are about an hour or so apart.

Actually....that is still useful. Meaning, if a person were out in a field, laying on a blanket and staring at clouds passing overhead, as carried by prevailing winds aloft? One hour of time can be extremely different, in terms of the clouds that may be observed. (AND our "normal" perception of time, and such).

The benefit of the 'time-lapse' videos (easily accessed on YouTube, for example) is that you can "fill-in-the-gaps" within an hour....depending on the setting OF the time-lapse sequence. (AS it is recorded).
 

Mackdog

Senior Member.
Looks great! It doesn't zoom as far in as Google Earth, but MODIS has 250 meter spatial resolution so you would not be able to see much more anyways. I guess the point of it is to view a much larger area than Google Earth. The revisit time for each MODIS is 16 days, but with both platforms it is 8 days..so it's still much better than Google earth for recent changes!

Just got done with my Remote Sensing 1 final exam today..so I'm nerding out :D
 

WeedWhacker

Senior Member
Approximately noon local time

Does it depend on the orbital trajectory of the satellite? (**) And, using "Noon" as a local reference time for the photo?

(Just 'spit-ballin' here....)

(**) or, I should say the "type of orbit". (This is really complicated, and of course "IS" 'rocket science'!!

Just to add an "excerpt" of how complicated it can be:

( I also know of a certain YouTube video that also illustrates and explains the above....but, I've posted it already on MetaBunk...so will not again. A simple 'search' will find it ).

(HINT: When you go to YT just "copy/paste" and enter this, in the "Search bar": Am7EwmxBAW8 )


ONE LAST "edit"? According to Apollo "lore"....'Buzz' Aldrin, second man to set foot on the Moon on the Apollo 11 mission was a HUGE "nerd" (what we call a 'nerd' today) when it came to understanding the physics of orbital mechanics. He dedicated much of his studies TO this....in order to best understand it.


"Orbital Inclination" is the term i was striving for. In regards to the satellites taking these weather photos. (Had to watch that YouTube Instructional Video....again!!!!). Worth a look, I promise!
 
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Ross Marsden

Senior Member.
Aqua and Terra are "sun synchronous". This means that they are more or less overhead at the same local time for everyone every day. They are also synched so that the the sun angle of the nadir is nice and high.
The net result is that Terra is overhead about 10am local, and Aqua is overhead at about 2pm.

On the night side of the earth, they are overhead at 10pm and 2am locals respectively.
 

WeedWhacker

Senior Member
"sun synchronous"

THAT is yet another "element" of 'orbital mechanics'....a LOT to learn and understand, "innit"???

Honestly....I have to watch that YT video over and over again....just to "begin" to grasp the science of orbits....and their 'mechanics' (which were worked out mathematically, centuries ago!!!).
 

Trailblazer

Moderator
Staff member
Aqua and Terra are "sun synchronous". This means that they are more or less overhead at the same local time for everyone every day. They are also synched so that the the sun angle of the nadir is nice and high.
The net result is that Terra is overhead about 10am local, and Aqua is overhead at about 2pm.

On the night side of the earth, they are overhead at 10pm and 2am locals respectively.

Thanks for that Ross, I was wondering the same thing.

You can access the MODIS imagery through this less user-friendly site, which does allow you to see the times the image swaths were taken:
https://earthdata.nasa.gov/data/near-real-time-data/rapid-response/modis-subsets


And the near-real-time (2.5 hour delay) images around the world here: https://earthdata.nasa.gov/data/nrt/visualization/rapid-response/modis-near-real-time-images


For me in the UK, this is the most useful page: http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=United_Kingdom_Ireland.2014345
 

Trailspotter

Senior Member.
Aqua and Terra are "sun synchronous". This means that they are more or less overhead at the same local time for everyone every day. They are also synched so that the the sun angle of the nadir is nice and high.
The net result is that Terra is overhead about 10am local, and Aqua is overhead at about 2pm.

On the night side of the earth, they are overhead at 10pm and 2am locals respectively.

Thanks for that Ross, I was wondering the same thing.

You can access the MODIS imagery through this less user-friendly site, which does allow you to see the times the image swaths were taken:
https://earthdata.nasa.gov/data/near-real-time-data/rapid-response/modis-subsets


And the near-real-time (2.5 hour delay) images around the world here: https://earthdata.nasa.gov/data/nrt/visualization/rapid-response/modis-near-real-time-images


For me in the UK, this is the most useful page: http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=United_Kingdom_Ireland.2014345

Both Terra and Aqua images are indeed taken about local noon, but the actual times vary significantly, depending on the place and the date.

Although the Aqua and Terra orbits are "sun synchronous", the satellites turn around the Earth in about 98.5 minutes each and do about 15 turns around the Earth per day. Also, they orbit the Earth in the opposite directions. The times of a particular area appearing in the image swath depend on its location and can vary by more than hour and half between the different dates for each satellite.

For the UK and Western Europe, the time differences between the Terra and Aqua passing vary from a few minutes to more than two hours.

The width of the image swaths is such that, for each satellite, there remain gaps near the equator, but closer to the poles the swaths begin to overlap, so that some areas can be seen by the same satellite twice a day. However, both Worldview and the MODIS subsets trim out the overlapping bits.
 
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Trailspotter

Senior Member.
Probably the fastest and least cumbersome way to find the times of Terra and Aqua images is to use the near-real-time link:
http://lance-modis.eosdis.nasa.gov/cgi-bin/imagery/realtime.cgi

You can change to an earlier date in the top left corner of the page. The Terra and Aqua 5-minute swath thumbs are in the top and bottom halves, respectively. The daily images are arranged in 15 or 16 vertical columns, representing individual turns of their orbits; the earliest turns on the right (East), the latest on the left (West). Within the individual columns the time increases from the top to bottom for the Terra swaths, and in the opposite direction for the Aqua swaths. Placing the pointer over a thumb displays the swath position on the globe that appears over the thumb below:
Screen shot 2014-12-12 at 18.59.38.png
This one is for the Terra swath at 11:20 UTC on December 1, 2014. Note that the actual swath is a bit longer in N-S direction and slightly wider in W-E direction. The Aqua image of the UK on that date was taken at 13:05-13:10 UTC:
Screen shot 2014-12-12 at 19.08.29.png

On the next day, December 2, some parts of the UK had been seen twice by Terra: at 10:25 UTC and 12:00 UTC, as well, as by Aqua: at 12:10 UTC and 13:50 UTC. On December 3, the times were: Terra at 11:05-11:10 UTC; Aqua at 12:55 UTC etc.
 
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Trailspotter

Senior Member.
I've just noticed that there have been no new Terra images since February 18, 2016 (the last, incomplete set). This includes the 'raw' data on http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/realtime.cgi?date=2016049.

I have not found yet any explanation to this. Was there equipment failure? Or, perhaps, the satellite has already been retired from service? Any information will be appreciated.

UPDATE

from the official Terra site in NASA: http://terra.nasa.gov/news/terra-is-in-safe-mode
Whatever this means.
 
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Mick West

Administrator
Staff member
Slightly more detail on Terra:
https://lpdaac.usgs.gov/about/news_archive/terra_satellite_enters_safe_mode
Basically: it's not working right, and they are trying to fix it. At least it sounds like they still have some control.

Best case is they installed some new software which caused problems. Worse case some piece of hardware is broken - either via wear and tear, or micrometeoroid. Terra is 17 years old.
 

Trailspotter

Senior Member.
The message has been updated, but its original date has not been changed. The new Terra images are available from yesterday, February 25, 2016 (or, for the Far West, the night before yesterday).
http://terra.nasa.gov/news/terra-is-in-safe-mode
 
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