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I've got lots of tiny streams on a hydrography shapefile. Historic texts indicate that certain ones have headwaters at "sources" or springs, and I want to try to find these. Browsing the historical imagery on Google Earth was my first attempt, but the ground cover and tree canopies are too dense to properly identify a pool. What kinds of satellite imagery types would help to identify such features?

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Ironically, the vegetation is likely to be thickest around spring sources, which is challenging for most satellite or aerial imagery. Perhaps LiDAR (or a bare-earth DEM derived from it)? –  Erica Jun 18 at 1:44
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Multiband imagery with an infra-red component. Not so much to spot the water but the lushness of the surrounding vegetation. This will be particularly prevalent in semi-arid areas like the Australian outback. –  Michael Miles-Stimson Jun 18 at 1:44

4 Answers 4

As someone who did feature capture from imagery for a while, I would caution you against expecting a pool at a spring. The majority of the ones I've encountered (both in capture and on the ground in person) don't have one. We often referred to ancillary sources to suggest/confirm a spring. Depending on your purposes, USGS quad sheets or hydrography datasets may prove useful.

As for imagery, time of year would be key. Imagery taken during spring or fall would be best - minimal snow and canopy/vegetation cover makes for better visibility. For this reason the US Ag Program (NAIP) imagery wouldn't be ideal, since their purpose is showing peak crop growth. Google takes their imagery from a variety of sources and it's rather hit or miss on time of year. I know some local county governments time their acquisitions to minimize canopy cover. Depending on your area of interest location, some times of the year may be better than others for spring activity/flow.

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I agree, pick the 'dry' time of the year where the presence of water will be highlighted against the background (green on brown depending on band selection), then go to the top of the green and there's the spring. Use of climate graphs/data will show where the dry season(s) are. –  Michael Miles-Stimson Jun 18 at 4:43
    
I agree with the seasonal timing issue, but for no-fee data, you probably won't beat NAIP for resolution (1-2m) and coverage, if you're AOI is in the US. Combining high-res elevation data with a CIR band combo should at least let you identify the source within a tolerance. Pinpointing a spring source exactly without a ground survey seems ambitious, but good luck! –  JWallace Jun 18 at 16:10

If you have tiny streams then you will want to have satellite imagery with better resolution than Landsat (30 meter pixels). However, Landsat has the best historical coverage. I would do a combination of imagery and elevation (DEM) data. Using a DEM to make a hillshade, or some hydro analysis (flow direction) will provide you a great combination of options to identify tiny streams and potential head waters that are much smaller than a 30 meter pixel. Otherwise you will be looking to get IKONOS or QuickBird four band imagery, which can get very expensive.

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Landsat imagery would be helpful. Different bands can be utilized separately or together depending on your needs, in your case delineating water and land boundaries would be near infared. If the streams are as tiny as stated, they may not appear due to the resolution or lack thereof.

Some links:

http://landsat.usgs.gov/band_designations_landsat_satellites.php http://landsat.usgs.gov/best_spectral_bands_to_use.php

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Landsat imagery at 30m or even the newer 15m resolution is unlikely to be much help in identifying a stream or even a small river, let alone a spring. Multiple bands and looking at IR (and the availability of historic data) are all positives, but the resolution issue pretty much kills it. You'd need something much higher as Ryan mentions. –  Chris W Jun 18 at 4:05

I have spent many years surveying rivers in the UK and have visited the sources of many streams. My experience in the UK a spring is rarely a pool of standing water but are "flushes", basically water seeping out of the ground. Springs could be swampy areas or heathland dominated typically with Juncus. But we do have the classic water bubbling out of the ground pools for sources (Eg. R. Itchen).

Such a feature as identified by the others is too small to capture or obscured by vegetation. You don't say where in the world you are working? If it was in the UK our national mapping agency supplies those annotations as part of MasterMap. You could convert those to a point and snap them to the nearest end point of a stream network, that would be a good first pass filter?

Also when you say spring are you talking about water seeping out of the ground or an Aquifer creating a pool?

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