[GLIMS] Landsat Next, and Landsat 7 refueling/repurposed mission

Mon Jan 4 09:06:15 MST 2021

Dear GLIMS colleagues,
This is a small update and also my request for you to do some advance thinking about a couple opportunities that might arise (but no guarantees).
I append to this message some relevant dialog.
First, it appears that we will have a chance to ponder and model the engineering specifics of the added sensor bands near 1 micron. I am most concerned about achieving the best tradeoff between bandwidth and signal:noise ratio; I am not convinced that the current amended plan has the best tradeoff; I'd go for slightly wider band full width at half maximum and improved signal:noise. To make use of the nailed-and-bracketed water and ice absorptions, we need the signal:noise ratio to support the radiometriic fidelity of reflectances in those absorptions. I will give some attention to this.
The second matter is where I am not the best person to weigh in on strongly. There is no guarantee that we will have a voice in the following matter (but if we don't try to exercise our voice we for sure have no voice): There might be a Landsat 7 refueling mission. The use of Landsat 7 after refueling is not determined. So my thinking is--if it is technically possible to achieve a repurposed Landsat 7 mission-- let's help determine it. I don't know the engineering constraints on Landsat 7 pointing and communications. Does the imager need to be nadir pointed in order for the communications system to be oriented correctly? I have no clue. It is indicated in the email dialog below that they almost lost Landsat 7 when they tried a pointed observation. Okay, that aside, what I would like to do is use Landsat 7 to obtain stereo data by flying it in formation with Landsat 8 for that express purpose. The best stereo, I believe, would be if Landsat 7 becomes forward looking, thereby complementing ASTER stereo. That way, the "back sides" of steep mountains could be covered. Let's say that off-nadir will be possible; they just need to get the engineering right so that it doesn't go into safe mode again. A question I have is-- assuming that off-nadir is possible-- how much usefulness would this system have for glacier studies and other mountain studies? Since there apparently will be some kind of satellite refueling mission, the possible choice of Landsat 7 for that might depend on having a good post refueling purpose, which of course could be just to continue that mission as it has been doing since 1999. But my view is that just continuing what it has been doing is not very advantageous, because its data are largely superseded by Landsat 8 and Sentinel.
Are there other ideas about what Landsat 7 could be used for? Shift it in time of day?
I have no idea whether we can have a strong voice in the Landsat-7 discussion, and no solid idea of what is technically possible. I was thinking that if we collectively put in just a little forethought about it, then when the time comes to speak to the Landsat 7 engineers and science team, then we will be somewhat matured in our ideas and suggestions.
--Jeff K

________________________________
From: Wu, Zhuoting <zwu at usgs.gov>
Sent: Monday, January 4, 2021 2:54 PM
To: Jeffrey Kargel <jeffreyskargel at hotmail.com>
Subject: RE: [EXTERNAL] RFI for Landsat Next 2020

Jeff,

We are still reviewing the RFI responses. The requirements for the mission won’t be finalized until the end of the year.

Z

From: Jeffrey Kargel <jeffreyskargel at hotmail.com>
Sent: Thursday, December 24, 2020 10:20 AM
To: Wu, Zhuoting <zwu at usgs.gov>
Subject: Re: [EXTERNAL] RFI for Landsat Next 2020

Dear Z:

Considering the added bands to nail and bracket ice and water absorptions near 1 micron, will there be further opportunity to work with the engineers to fine tune the bandwidth and signal:noise requirements before sensor designs are set in stone?

And: Merry Christmas!

Cheers,

Jeff K

________________________________

From: Wu, Zhuoting <zwu at usgs.gov<mailto:zwu at usgs.gov>>
Sent: Friday, November 27, 2020 4:09 PM
To: Jeffrey Kargel <jeffreyskargel at hotmail.com<mailto:jeffreyskargel at hotmail.com>>
Subject: RE: [EXTERNAL] RFI for Landsat Next 2020

Jeff,

There’s a re-fueling mission, used to be called “Restore-L”, now “OSAM-1”. Landsat 7 is the currently the primary refueling mission candidate, but it depends on how much fuel L7 has left before OSAM-1 is ready to be launched. It’s a technology demonstration mission instead of restoring L7 science capability. There’s no firm plan regarding how L7 will be used if L7 is the candidate for OSAM-1 and if the refueling is successful. We’ll have this discussion when things get closer.

Thanks,

Z

From: Jeffrey Kargel <jeffreyskargel at hotmail.com<mailto:jeffreyskargel at hotmail.com>>
Sent: Thursday, November 26, 2020 6:48 AM
To: Wu, Zhuoting <zwu at usgs.gov<mailto:zwu at usgs.gov>>
Subject: Re: [EXTERNAL] RFI for Landsat Next 2020

Z: I understand that there has been discussion of a robotic refueling of Landsat 7. Has there been any discussion of moving it to fly in formation with Landsat 8, behind Landsat 8, possibly to have a small fore-looking angle to provide stereo? This would complement ASTER's band 3 aft-look and would allow improved topographic models of mountainous terrain, and it would allow stereo data continuity after ASTER is decommissioned. It would not be the best stereo (considering SLC-off), but it would be better than having a gap in stereo acquisitions after ASTER or being solely reliant on commercial smallsats for stereo. Having a different look angle would also help with multi-angle radiometry (bidirectional reflectance) of flat-lying regions, like ice sheet plateau surfaces and Amazon rain forest. The off-nadir look might have some risk-- you mentioned a scary safe-ing event, but with an old satellite, the risk would be reduced, as a potential loss would be less impactful. I mentioned before the role that simultaneous stereo (as distinct from ASTER's 40 seconds-apart stereo pair) could have for new applications to second-to-second dynamic phenomena. A fully repurposed Landsat mission would extend Landsat science applications, whereas refurbishing Landsat 7 but leaving it as-is would provide inferior data to Landsat 8 and not really offer anything substantially novel or even useful. And if Landsat 8 and 9 would fail (worst case), Landsat 7 would still be there, hopefully, to resume a normal Landsat mission's way of nadir mapping in preparation for Landsat 10.

Just a thought. Maybe errant thinking, I don't know.

Cheers,

Jeff K

________________________________

From: Wu, Zhuoting <zwu at usgs.gov<mailto:zwu at usgs.gov>>
Sent: Saturday, November 21, 2020 9:48 PM
To: Jeffrey Kargel <jeffreyskargel at hotmail.com<mailto:jeffreyskargel at hotmail.com>>
Subject: RE: [EXTERNAL] RFI for Landsat Next 2020

Jeff,

I’m probably not the best person to answer this. Our Flight Ops team should know this. In principle, Landsat 8/9 is not doing any off-nadir acquisition even if there’s an emergency/disaster need, as Landsat is not designed for emergency response. As you know, Landsat 8 went to safehold mode last year while initiating an off-nadir nighttime imaging attempt.

Z

From: Jeffrey Kargel <jeffreyskargel at hotmail.com<mailto:jeffreyskargel at hotmail.com>>
Sent: Saturday, November 21, 2020 12:33 PM
To: Wu, Zhuoting <zwu at usgs.gov<mailto:zwu at usgs.gov>>
Subject: Re: [EXTERNAL] RFI for Landsat Next 2020

Z:

Just a quick question, which either has a yes or no that you may know immediately, or possibly is not known yet. In principle is Landsat 8, and will Landsat 9 be, able to point the entire spacecraft to off-nadir (15 or 20 degrees along-track), and still be able to communicate and maintain thermal and attitude stability?

--Jeff Kargel

________________________________

From: Wu, Zhuoting <zwu at usgs.gov<mailto:zwu at usgs.gov>>
Sent: Friday, November 20, 2020 7:53 PM
To: Jeffrey Kargel <jeffreyskargel at hotmail.com<mailto:jeffreyskargel at hotmail.com>>
Subject: RE: [EXTERNAL] RFI for Landsat Next 2020

Hi Jeff,

I got your letter and will pass along to the USGS/NASA team. We haven’t started reviewing the RFI responses yet, so this letter will be considered. Thank you for sending in the response!

Thanks,

Z

From: Jeffrey Kargel <jeffreyskargel at hotmail.com<mailto:jeffreyskargel at hotmail.com>>
Sent: Friday, November 20, 2020 12:47 PM
To: gsfc-landsatnext-rfi2020a at lists.hq.nasa.gov<mailto:gsfc-landsatnext-rfi2020a at lists.hq.nasa.gov>
Cc: Wu, Zhuoting <zwu at usgs.gov<mailto:zwu at usgs.gov>>
Subject: [EXTERNAL] RFI for Landsat Next 2020

 This email has been received from outside of DOI - Use caution before clicking on links, opening attachments, or responding.

Dear Landsat-Next RFI response evaluators:

Following my submission of a response to the recent RFI, a great deal of conversation erupted within my glaciology community, with hearty endorsement of the idea of incorporating a stereo imaging capability. We recognized that this is not a trivial augmentation and that any such augmentation should serve far more than the glaciology community. Therefore, a few of us wrote up our ideas in a bit more specific form than I had done in my response to the RFI. We then organized an outreach effort to secure the views and endorsements of scientists covering a wide range of the Earth sciences. It is heavy on the glaciologists' endorsements only because that is the field we know best. But we can assure that the response is just as enthusiastic among those in other Earth science fields where topographic measurement would be important. We have taken both a minimalistic approach and a sky's-the-limit approach, so as hopefully to stir some conversation within your Landsat-Next planning and engineering group.

So of course we apologize-- I specifically apologize-- for not having motivated this depth of  conversation prior to the official due date for responses, but I do think that you may find it interested to see a bit of the global eruption of enthusiasm for Landsat 10 and the possibilities.

Below is the letter.

Sincerely,

Jeffrey S. Kargel-- on behalf of the cosigned

Senior Scientist

Planetary Science Institute

Tucson, AZ

520-780-7759

jeffreyskargel at hotmail.com<mailto:jeffreyskargel at hotmail.com>

jkargel at psi.edu<mailto:jkargel at psi.edu>

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