Hi Supriti:

I am not familiar with the river Sundarbans, but the answer will change with the size of the river.

SRTM is not going to give you the bathymetry of the river though.

A rule of thumb would be to look at the size of the features you are looking to record, map and see what kind of imagery provides data at the right scale.

As Rosemary wrote, it all depends on the scale at which you work.

Good luck

Chris

I think you can compare if the resolution of SRTM is sufficient to the analysis of the river, cause 90 meters can mask the changes. However, you can looking for high resolution MDE data, such as ALOS, ASTER, among others satelite.

Hi!

In my opinion SRTM will not be useful for You, because of it's poor resolution (90m x 90m). Of course everything depends on scale which You work, but for river morphometry useful will be topo-maps (1:10,000) and similar DEM resolution (i.e. ASTER GDEM 30m x 30m). Maybe for Your study area there are good topo maps or free DEMs, You have to find them!

Regards!

Bart

As others have mentioned it would be useful to figure out first of all what is the minimum size of area on the ground that you want to map and the whole size and scale of your study area? Sundarbans is definitely not the easiest place on earth to study obviously because of being the largest mangrove forest in the world with a very complicated network of streams, rivers, deltas etc. Are you studying the whole of Sundarbans or part of it? Generally for any remote sensing study it is advisable to first make a note of the properties of the object on the surface of the earth that you are interested in like size, shape, area and other characteristics and then look for appropriate tools to match with their attributes .You may definitely have to take into account the temporal and spatial resolutions, if not the spectral and radiometric. The accuracy of the DEM may be another factor which you may have to consider. You can check with the Survey of India (SOI) database for large scale topo maps of the area. Have you checked if there are any previous studies done in the same area? If yes, then how did they do it?

Hi Supriti,

Above all answers give you a clear idea , how you need to proceed to the analysis.

I would like to suggest you that, you can use the SRTM data of 30X 30m resolution ( freely available in http://earthexplorer.usgs.gov/).

For the profile study, if you are taking the longitudinal profile, it will give good representation. similarly for the cross profile also you can use the 30m SRTM but be assure that, the width analyzing channels .

I dont think you can heavily depends on the satellite images for the temporal bathymetry ( but you can use the satellite images for the identification of width changes in different periods),

For the temporal depth data, you need to consult with the Govt. organizations  monitor the characteristics of rivers. 

Research papers in channel morphology using SRTM data is attaching for your reference.

Hope this will help you ..

Good luck in your research..

If you want to analyse the changes in depth and width of river channel over the years, then SRTM won't help with that, no matter the resolution...(It is not possible).

You may want to try any or a combination of any of the high resolution imageries by GeoEye, IKONOS, ASTER, AVHRR etc. to determine the width of the channels temporally.

To determine the depth of a river channel over the years, you may have to visit the agency in-charge of monitoring the water body you are interested in. SRTM may appear useful here once, but not on a temporal scale as you would expect; this is because SRTM data is not available for each year.

Hi Chinedu,

                    Thanks. Finally you've got my question. I want to analyse the changes in depth and width of a river channel over the years. But the problem is there is no such agency for monitoring water bodies at Sundarbans. A very little works has been done in the rivers of the Sundarbans except the Hugli/ Ganges. So, I have to depend fully on the satellite images. Since GeoEye, IKONOS and AVHRR etc. are not  freely available and I am not sure about the quality of the images as I am pretty sure that there will be voids in the imagery so may I use Google earth image? 

Moreover only one year SRTM  and ASTER data is available. I have topographical sheet of 1972 and the Google Earth has imageries since 2006 of the respective area. So, may I use SRTM, ASTER, GoogleEarth and topographical sheet(1:50,000) toghether to compare them? I will also conduct  direct measurement at field. Would you like to tell me about this?

I am looking forward to listening to you.

Thanks

Supriti

Thanks to all of you for answering.

I would look to see the availability or possibility of combining existing LIDAR project products already performed along the Ganges. Perhaps then you could build a phone app with which to sample the depth through crowd sourcing methods, i.e. volunteers with cell phones bathing or swimming at various points.

https://www.google.com/search?q=india+lidar+project&ie=utf-8&oe=utf-8

Once Lidar info can be obtained, you can turn this into a DEM in Arc Map and then determine slope, flow direction of the terrain and project current creek paths. This could be available at a resolution of 1 ft. Its only a matter of time, or money.

Hi Supriti,

Your thoughts are in order. You have a good idea as to how to go about your research, under the circumstance.

Google earth acquires its imageries from high resolution imageries providers, like some of those you already know. So you can rely on it, and compare as you've stated above.

Determining the width of the channel for the selected years you wish to consider, won't be much of a problem. But determining the depth, would certainly be a little difficult with uncertainties, as these imageries do not give a true reflection of depth.  The use of LIDAR dataset is a promising alternative, but its availability for your area of study is another question.

If you must do this anyways, i suggest you use the channel parameters you could derive from the topographic sheet (1:50,000) for 1972 (1st year), and then use the SRTM DEM for the year 2000 (2nd year), the ASTER GDEM for 2009 (3rd year), and then, your field measurement data (the most recent you'd have; say 2016 (4th year)). So, you would be looking at changes in the morphometric parameter of interest, based on these four time frames or any other set of time frames you choose to use.

The pitfall here (which should be avoided) is that these datasets are not at the same scale, and the time interval is not uniform. If you could live with that, it's up to you.

Lastly, to perhaps avoid the pitfall mentioned above, you might have to generate for yourself, several DEMs or Topographic models representing different times, from Radar data, such as SAR, and use them in addition to your 1972 toposheet (if you like).

I wish you success.

Aster or USGS DEM

Hy Supriti, for Depth i agrre with Yizhou, you can use Aster DEM or LIDAR, and for the width can use Landsat 8 (50 m x pixel), its depens about de river width.

Regards

Hi Supriti Bose

I think the Aster or the USGS DEM are beter for your problematic.

However, you can get river profile ( small rivers) from DEM. for the depth.

Best wishes

I hope, Cartosat DEM also useful for your studies, You may try with Carto DEM

Supriti

Given your tidal interests in the Sundarbans have you seen the following (see attached):

Managerial response to sea level rise in the tidal estuaries of the Indian  Sundarban : a geomorphological approach

Somenath Battacharya[1]; John Pethick [2]; & Kakoli Sensarma.[3]

In this paper there is a very good exposition of tidal regime modelling and the associated changes in sedimentation up the various blind rivers of the Sundarbans through estuary dynamics. Also considers how sea level rise would affect the system.

It has been published :

Bhattacharyya, S., Pethick, J., Sensarma, K., 2013. Managerial response to sea level rise in the tidal estuaries of the Indian Sundarban: a geomorphological approach. In: Xun, Wu, Whittington, D. (Eds.), Water Policy Journal: Special Edition: The Ganges. Basin Water Policy, 15, pp. 51–74.

I am currently in Kolkata, but had no chance to revisit the Sundarbans.

Rgs

Julian 

Thank you so much, sir.