agraham1 Posted February 20, 2015 Report Share Posted February 20, 2015 Hi all, Just a question regarding the fundamentals of sensor channels. Its surprisingly hard to find any info about this online- and in journal articles. Lets say I have two multispectral sensors- each with a red edge channel: 680-730nm 710-720nm What I am wondering is whether for broader channels, like #1, does the reflectance represent an average over that spectrum? I have always assumed it does. In which case, it would be better to have a couple narrow channels in the red edge spectrum to fill out the red edge curve. #1 would then not be ideal because you wont be able to quantify the start and end of the curve- is what I am thinking. Let me know your thoughts. Quote Link to comment Share on other sites More sharing options...
Bruce1807 Posted February 22, 2015 Report Share Posted February 22, 2015 You are right. It is an average. As for your second part it depends on what you trying to do. Certain objects reflect over an entire band like band 1. If you use band 2 you will not get an accurate picture. If you use multiple bands that have all the items of band 1 then what. will you then just average them out? In theory you should get the same result. In practice you wont because of response curves etc. but it will be pretty close. Basically it comes down to what are you trying to do? Quote Link to comment Share on other sites More sharing options...
agraham1 Posted February 23, 2015 Author Report Share Posted February 23, 2015 Hi Bruce, Thanks for your reply. In respect to leaves- you get high chlorophyll absorbance in the red, low in the NIR which make up the red edge- and I want to map this whole curve. But if I'm getting an average from Band 1, I may only get an average reading somewhere along the curve- I wont have to low and high values. Quote Link to comment Share on other sites More sharing options...
Bruce1807 Posted February 23, 2015 Report Share Posted February 23, 2015 Ok I see what you are trying to do. Be a little careful if you are presenting this as a paper or thesis, unless of course that is what it is about. Make sure you can validate your results. Also some plants have a different or broader range. I think (if my memory is correct, although this is far from my specialist subject) needle leaves like pines have a broader range than flat leaves. The hyperion datasets, which have 200 + bands, let you really nail down some stuff. Brilliant for coral reefs, but validation takes a lot of ground work. In my case many hours under the water. 1 Quote Link to comment Share on other sites More sharing options...
agraham1 Posted February 23, 2015 Author Report Share Posted February 23, 2015 Hey Bruce well, I have a spectrometer handy in the lab so I will be able to fill out the red edge for comparison... it is not however my thesis. I am more looking at canopy chlorophyll response as an indicator of stress in wheat. Anyways, do you use hyperspectral imagery to analyze coral reef health? That really sounds incredible! Quote Link to comment Share on other sites More sharing options...
Bruce1807 Posted February 25, 2015 Report Share Posted February 25, 2015 Actually my job is only about 20% GIS work and reef stuff I'm doing in my own time with a little support from a few friends that love to dive as well. Lots of underwater photography.. Using the GPS of the boat then geettining the errors of the UNAVCO stations to try and get pixel boundries as close as possible. We drop a plumb line from the boat as our reference point and then try and map map out a pixel and survey and photograph the amount of coral, the species and the health. We often mark the site and then go back around midnight and do a once over to see the coral feed. It gives a great indication of whats going well. The only problem is that the sharks are all just out of the divelight range and they are waiting for the lights to fail. All fun. Unfortunattly EO-1 is in a decaying orbit as it is out of fuel. It is expected to last till September and getting anything new tasked wont be easy, although I have requested it through https://eo1.usgs.gov/dar/form I will see if it gets done before its demise or in real terms "burn & crash" The below article follows on about the future of these hyperspectral missions. The Status of HyperSpectral Missions The sub-title to this post could easily be “reasons to love DLR #123 (transparency)”. You’ll see why in a moment. In this post I am going to do a very brief review of the civilian hyperspectral (or imaging spectroscopy) missions, operating or planned for the near future, that will provide Earth Observation (EO) data. Let’s start in the past. Hyperspectral imagers (HSI) were first launched into space at the start of the millenium. First NASA launched Hyperion on the EO-1 platform in 2000, then ESA launched CHRIS on Proba in 2001, kick-off an exciting new millenium of advanced EO platforms. And there it all stopped. Both were technology demonstrators. Hyperion and CHRIS still sporadically collect data, but only rarely and not with anything near global coverage. Both sensors were plagued by poor data quality but they were, and are, the best we have. Experience with these missions has fuelled arguements that HSI is best left to aircraft flying below the bulk of the atmosphere and a range of companies now offer high quality sensors that allow you to do that. Jump forward to the mid-2000s and scientists and engineers began to release plans for new spaceborne missions. HSI was just to attractive to ignore. Three proposals received a lot of attention: the Italian PRISMA concept developed by ASI, Germany’s EnMAP and NASA’s HyspIRI concept. ASI has clearly decided to ficus on SAR (COSMO-SkyMed) and hyperspectral missions; PRISMA entered Phase A (design) in 2007. EnMAP was close behind and cleared critical design review in 2010. NASA’s HyspIRI has a slightly different evolution having been proposed by the first Decadal Survey of Earth Sciences. This argued for the need for an HSI to follow on from Hyperion. Operations were tenatively slated for 2013-2016. This is where things get messy. ASI’s deadlines for PRISMA began to slip. Information flow on the status of the mission is relatively poor but updates leak out occassionally. According to Lopinto and Ananasso (2013) launch is scheduled for 2017. However, Staenz and Held suggest PRISMA has been de-scoped suggesting a 2017 launch might be optimistic. ASI still claim a 2015 launch is planned; clearly this is just an outdated website. What is going on at ASI is therefore hard to parse. In contrast EnMAP development seems to be going well. Launch is scheduled for 2017 and the mission is in the final preparation phase. To be fair the original plan was for a 2015 launch but then almost all satellites launch late. The great thing about EnMAP (and DLR) is the transparency. This leaves us with HyspIRI. This will take a longer post at a later date. Suffice to say, HyspIRI isn’t going anywhere soon. The Decadal Review’s envisaged 2013 launch has been pushed back, and back, and now seems to be sometime after 2022. Given the atmosphere in Congress and the fight over budgets (see previous post), no one can guarantee a program will be progress to launch. I’d not gamble on HyspIRI even though I think it’s a great mission and an important evolution of multispectral imaging. Essentially we are reading tea-leaves here. That leaves us with a surprising outsider that might pip all the challengers to the posts. The Japanese space agency JAXA has been developing the HISUI HSI sensor for launch on ALOS-3. In my experience HISUI han’t received as much attention as the other missions mentioned, possibly because Japanese engineers and scientists tend to publish in Japanese (though not exclusively). ALOS-3 has a launch schedule around 2015, though we can expect that to slip (if my infomation is not already out of date). The ALOS-2 project manager, Yuji Osawa, has stated that JAXA would like to seen an overlap in operations between ALOS-2 and -3 so a 2015 deadline, or shortly thereafter, is not inconceivable. Regardless, we should have an HSI mission launched in 2017 at the latest, with hopefully a launch before then. Another reason to cheer ALOS-3 is easier access to data. EnMAP will probably be run on a more commercial basis with limited data available to science. JAXA and ESA have a history of collaboration and so we might expect easier access to ALOS-3 HISUI data. ASI I have no experience of, but COSMO-SkyMed data has not proven particularly easy to access. Quote Link to comment Share on other sites More sharing options...
agraham1 Posted March 3, 2015 Author Report Share Posted March 3, 2015 That is some really awesome stuff you are doing. I am now wondering the application of underwater rovers equipped with hyperspectral sensors to detect coral health. We have an underwater rover at the university- its a great idea for a future study- once lightweight hyperspec. sensors become cheaper! Quote Link to comment Share on other sites More sharing options...
Bruce1807 Posted March 3, 2015 Report Share Posted March 3, 2015 (edited) What I want for my birthday www.itres.com/wp-content/uploads/2014/10/U10077-00_uVNIR-1920.pdf Edited March 3, 2015 by Bruce1807 Quote Link to comment Share on other sites More sharing options...
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