Another Q: Landsat equatorial crossing time?

Tuesday, October 30, 2012 at 08:07:52

I had another good question in class last week as to why the Landsat missions have/had a ~10am UTC equatorial crossing time. In fact the full list of satellite times are below (Source: wikipedia):

Landsat 19:30 AM +/- 15 minutes
Landsat 29:30 AM +/- 15 minutes
Landsat 39:30 AM +/- 15 minutes
Landsat 49:45 AM +/- 15 minutes
Landsat 59:45 AM +/- 15 minutes
Landsat 710:00 AM +/- 15 minutes

So why is that? Although I didn’t know, I thought it was something to do with optimum reflectance from the Earth’s surface in relation to the original mission objectives, and that it’s stuck ever since

I’ve asked a couple of colleagues and the consensus seems to be to acquisition (globally) of “good”, usable, imagery but that it’s a trade off between about solar elevation angle, cloud formation and dew/frost cover. As you see from the table above, later Landsats have progressively gone for slightly later times.

Some further comments include because it places the local time for most of the imaged land areas (primarily in the northern hemisphere) in the 10am-2pm range when the sun is at a high elevation (in order to minimize shadow). Additionally, there is a consideration for cloud. “Conventional wisdom” is that we avoidthe afternoon buildup of cumulus clouds over interior regions with the10am crossing time. This doesn’t necessarily help out in coastal areas though.

Thanks to those who answered my query and any further thoughts would be welcome!

Satellite imaging at night

Monday, October 29, 2012 at 08:52:46

I was asked in-class this week about imaging the Earth’s surface at night…… does it happen? The short answer is yes, it can, but generally doesn’t for much of the Earth-resource imaging that takes place. Here are some instances where it does (and I’m using examples from the fantastic NASA Earth Observatory Image of the Day):

Astronaut photo: plenty of examples using a standard digital camera with a short focal length, wide f-stop and high ISO. I like this one of northern Europe (Nikon D3S digital camera using a 28 mm).

Thermal Imagery: if there isn’t much visible light around, use a different part of the EM spectrum. Thermal wavelengths are commonly monitored, such as this image of a lava flow in Chile.

Microwave Imagery: thermal imagery uses naturally occurring raditation at longer wavelengths than visible light and the strong contrast (at night) to the surrounding terrain allows “hot” objects to be visible. Microwave, in contrast, is at much longer wavelengths (mm to cm) and uses energy generated by the satellite to illuminate the Earth’s surface. This allows it to operate at night (and through cloud). I couldn’t find any nighttime examples, but this one shows an oil spill off South Korea.

NPP Day/Night Mode: NPP VIIRS (see earlier blog) has a day-night band (wide bandwidth) and can therefore operate at night to image clouds (particularly when there is moonlight) and auroras (EOID explanation). A good image of Hurricane Sandy.

These are them most common nighttime imaging techniques you’ll come across, however most Earth surface remote sensing is achieved using a sun-synchronous orbit and so not at night.

Livescribe in action

Saturday, October 20, 2012 at 19:14:26

Following on from my last post introducing the LiveScribe pen I wanted to highlight some useful resources and functions, as well as demo my first two “pencasts”. So, without much ado:

-at it’s simplest this is making your notes/recordings available online either as a Flash animation or interactive PDF
-the PDFs work great and an incredibly effective way to distribute notes
-there is an iPhone app, but no Android app. This is an almighty cock-up because Livescribe have been banking on Flash working on Android - which it doesn’t. So at the moment, Livescribe doesn’t work on Android
-look at other peoples’ training notes to get a feeling for the scope

Pencasting(with some tips culled from the Advanced Pencasting webinar):
-however pencasts are very exciting for the production of training materials. They in essence allow you to produce, with little time or expertise, a live animation. You essential create a “performance” of the learning materials you want to develop. The flexibility in pencasting (albeit with some restrictions) are amazing
-write a script - I’ll say it again, its a performance
-keep it short 1-3 minutes MAXMIMUM, one page only. They are learning “bites”
-write (draw) first, narrate later. You speak faster than you write
-this highlights one of the exciting aspects of pencasting - when replaying the audio your drawings are synced to them. This massively extends the creativity of the pencast
-pre-draw elements in ordinary pencil on the page; you then get it “right” on your first “take”
-think about your presentation page design in terms of (1) layout and (2) navigation points. You want your material to be easy to follow, visually appealing and have visual cues so viewers know where to click to access different parts of the audio
-pre-draw (with the Livescribe pen) “templates”; these remain static and visible from the beginning (in black) meaning you can animate around them with your audio synced
-“pause and pop”: record, pause, draw, re-start (tap pause to continue). This causes the drawing to “pop” within the synced audio. Visually effective
-“Annotations”: draw your marker, record your audio, stop. Then playback and add your drawing. As I noted above, drawings added on playback are synced to the audio!! It’s worth stopping and taking that in - it is an incredibly powerful feature
-“Simuls”: take the annotations idea and continuously replay your audio to allow you to draw and build up your animation
-Marker Page: when using the “Simuls” approach, each time you playback you touch the marker on your dot-paper. Put the audio on a second page and your drawing on the first page. This stops all your dots appearing. When you export the first page as a PDF all the audio will be with it.
-as promised my first two pencasts. They are a long way from perfect but hope you get the idea:
Basic Wave Theory (including the accidental typo!)
Particle Theory

SmartPen101: online training
Webinar Recordings: recordings of live training the intro and advanced pencasting are worth viewing if a little long winded at times.

Livescribe Echo Pen

Saturday, October 13, 2012 at 08:37:52

Over the summer I bought a Livescribe Echo Smartpen to try out some digital note taking (a review and on Amazon). Believe it or not, I like writing and smartphones don’t cut the mustard here, whilst tablets still have a way to go to beat the convenience of paper. The Echo particularly caught my eye as it integrates audio recording in to the digital note taking which in my mind makes it a killer combination. Sit in a lecture and take notes whilst recording the audio. Want to hear what the lecturer was saying when you were writing a particular note? Simply tap the paper at the point and it starts playing it. Audio ceases to be purely linear with a content timeline mapped out in your notes making it very easy to access. You can also upload your digital notes (and audio) to the desktop application and, wonderfully, you can search for words in your text (clearly it does some handwriting recognition behind the scenes) and also convert the writing to text (but using the extra “paid-for” app).

How does it work? Well digital note taking on paper falls in to two categories - a clip on IR sensor that works on any sheet of paper or special dedicated paper that allows the pen to know which page you are on and where. Livescribe use the latter approach with a small camera in the tip of the pen that records the ink trace and compiles the 2D coordinates in to your handwriting. This means you have to buy Livescribe notebooks - I find this fine and think the product is very reliable as a result. Combined with the audio (and you can get a directional mic to plugin!) it is a killer product in the note taking market. In a business meeting a need a formal written/audio record? Use Livescribe? Clerking a meeting? Livescribe. Legal ramifications (lawyer, education etc) - Livescribe.

The basic pen comes with 2Gb of memory - not much if you want keep all your recordings with you but more than enough if you record, upload and store. And its cheap at ~70 in the UK (recent price drop), although Livescribe themselves have gone very quiet which suggests a product range revamp.

I use it for
-use it for recording a lecture and making notes
-use it for taking notes from books
-convert writing to text (MyScribe plugin)
-user it to create multi-media animations

More in a follow-on blog entry.

Reuters remote sensing links

Thursday, October 11, 2012 at 12:40:12

A slew of Reuters remote sensing links which is quite refreshing. Possibly worth pointing out that we are now in the middle of World Space Week, not that you’d know it! Amazingly it was established by the UN and has been running since 1999 - I’ve only just spotted it now thanks to a great info piece from the BBC about DMC. Anyway, back to the news:

SpaceX Rocket Glitch: big news that SpaceX had its first commercial cargo mission to the ISS, with a secondary mission to deploy a satellite. A partial engine failure on launch led to a failure to meet orbit and so deployment of the satellite in the wrong orbit. C’es la vie!
SpaceX Success: but the built in redundancy means that it still made its primary objective of ISS resupply.
China Mars ambitions: China has firmly set its sites on Mars with a plan to bring back a sample from the surface. Exciting times.

QGIS Plugins

Tuesday, October 9, 2012 at 07:05:28

I was presenting at the Society of Cartographers last month (on LAAP for those interested). Mike Shand gave an “Introduction to QGIS” (some helpful links on that page) which reminded me that I had wanted to do this blog post…..namely that “as it ships”, QGIS is pretty powerful but if you want to run through a complete project workflow you’ll rapidly find yourself up against a brickwall. It’s not that it can’t do much geospatial processing, but rather a lot of this functionality comes as plugins that have been developed separately. My MSc students hit this in their spatial analysis module - they perform an analysis in ArcGIS and then re-do it in QGIS. So this year I asked them to collate a list of “must have” plugins. So here it is and please feel free to suggest additions:

1. fTools: vector data analysis and management
2. Table Manager: edits and deletes shapefile columns
3. Spatial Query: conduct spatial queries on vector layers
4. Plugin Installer: download and install python plugins
5. MMQGIS: manipulates vector map layers, including alot of CSV functionality.
6. SEXTANTE: provides front ends to SAGA, GRASS, Orpheo Toolbox, MMQGIS etc. Think ArcToolbox for QGIS (to be rolled in to QGIS 2.0)

Sometimes there is an issue with a particular build so its always worth trying the master nightly build over at the QGIS Wiki.

BBC In Our Time

Monday, October 8, 2012 at 08:07:18

OK, think I’m a little slow to the party on this one (and not a great radio listener) but the BBC’s “In Our Time” presented by Melvyn Bragg is a great “ideas” discussion programme (Wikipedia entry). Just look through the archive which features all episodes from the first in 1999 as well as an RSS feed for all episodes since 2011. Donald Clark notes the power radio for dissemination; thiss is ideally suited to learning and, in combination, with internet playback/recording means you can save and review. Perhaps I’m just not particularly a radio fanboy, but I do quite like listening to podcasts so it may be more a case of marketing than anything else. Not easy in a crowded marketplace.

Anyway, well worth a look at the archive and Ill be pointing my students to the broadcast on Radiation.

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