NASA Uses Moonlight to Improve Satellite Accuracy

From NASA


NASA’s airborne Lunar Spectral Irradiance, or air-LUSI, flew aboard NASA’s ER-2 aircraft from March 12 to 16 to accurately measure the amount of light reflected off the Moon. Reflected moonlight is a steady source of light that researchers are taking advantage of to improve the accuracy and consistency of measurements among Earth-observing satellites.

“The Moon is extremely stable and not influenced by factors on Earth like climate to any large degree. It becomes a very good calibration reference, an independent benchmark, by which we can set our instruments and see what’s happening with our planet,” said air-LUSI’s principal investigator, Kevin Turpie, a research professor at the University of Maryland, College Park. 

The air-LUSI flights are part of NASA’s comprehensive satellite calibration and validation efforts. The results will compliment ground-based sites such as Railroad Valley Playa in Nevada, and together will provide orbiting satellites with a robust calibration dataset.

NASA has more than 20 Earth-observing satellites that give researchers a global perspective on the interconnected Earth system. Many of them measure light waves reflected, scattered, absorbed, or emitted by Earth’s surface, water and atmosphere. This light includes visible light, which humans see, as well as invisible ultraviolet and infrared wavelengths, and everything in between. Like musical instruments in an orchestra, the individual satellite instruments need to be “in tune” with each other in order for researchers to get the most out of their data. By using the Moon as a “tuning fork,” scientists can more easily compare data from different satellites to look at global changes over long periods of time. 

This cartoon of the electromagnetic spectrum shows how energy travels in waves; Humans can only see visible light, but the entire spectrum is used by NASA instruments to observe Earth and more.
This electromagnetic spectrum shows how energy travels in waves; Humans can only see visible light, but the entire spectrum is used by NASA instruments to observe Earth and more. Credits: NASA

That’s where air-LUSI comes in. Developed in partnership with the National Institute of Standards and Technology (NIST), U.S. Geological Survey and McMaster University, air-LUSI is a telescope that measures how much light is reflected off the lunar surface to assess the amount of energy Earth-observing satellites receive from moonlight. It was mounted aboard the ER-2 aircraft managed by and flying out of NASA’s Armstrong Flight Research Center in Palmdale, California. The ER-2 is a high-altitude aircraft that flew at 70,000 feet, above 95% of the atmosphere, which can scatter or absorb the reflected sunlight. This allowed air-LUSI to collect very accurate, NIST traceable measurements that are analogous to those a satellite would make from orbit. In order to improve the accuracy of lunar reflectance models, air-LUSI measurements are accurate with less than 1% uncertainty. During the March flights, air-LUSI measured the Moon for four nights just before a full Moon. 

This airborne approach has the advantage of studying moonlight during different phases of the Moon while being able to bring the instrument back between flights for evaluation, maintenance, and, if necessary, repair.

The cylindrical air-LUSI telescope is positioned to measure a simulated Moon at the far end of a laboratory for testing and calibration before and after the flight campaign.
Shown is the air-LUSI telescope positioned to measure a simulated Moon in a laboratory for testing and calibration before and after the flight campaign. Credits: Kevin Turpie

Making Improvements for Better Accuracy 

The air-LUSI spectrometer is hermetically sealed within an enclosure that keeps the instrument constantly at sea level temperature and pressure. Light collected by a telescope enters an integrating sphere which directs the light to the spectrometer, which is an instrument that measures variances of light waves. The air-LUSI first flew in similar flights in November 2019. Since then, the air-LUSI team has continued to improve the instrument’s accuracy.  

The team improved the internal monitor so they can better check instrument accuracy over a greater range of wavelengths, from the ultraviolet to the near infrared. They were also able to redesign the integrating sphere to remove small effects of changing temperature. 

“This will help the instrument make measurements with the more than 99% accuracy levels we’re looking for,” said Turpie. 

Making these changes was challenging. Delays from the COVID-19 pandemic caused the chief engineer, who was working on the instrument updates and repairs, to develop a new remote work plan. Both he and the principal investigator received special permission to have parts delivered directly to their homes so they could work on the instrument and be prepared for the 2022 flights.

Using the Moon as a Common Standard

The data from 2019 and 2022 together has the potential to assist scientists in making Earth-observing satellite data in the ultraviolet to near-infrared range more consistent. In addition, the common Moon standard would make it easier to compare and fine-tune current and future satellite observations. NASA’s upcoming Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission is planning on using the Moon as a common benchmark to make its observations more accurate and inter-consistent with other satellite measurements of Earth. Over the next decade, PACE and the future orbiting sensors of NASA’s Earth System Observatory will help create a more cohesive picture of our planet.

“Having a common calibration source outside of the Earth will help us reach this objective,” said Turpie. “Once air-LUSI measurements are used to improve the accuracy of the total amount of light coming from the Moon, we can take extensively more accurate measurements of Earth using current and future space-borne observatories.”

Banner Image: NASA’s ER-2 aircraft shown ready for fueling and flight preparations. Photo Credit: Ken Ulrich

By Abby Graf
NASA’s Earth Science News Team

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lee
April 4, 2022 10:27 pm

“The results will compliment ground-based sites” You are a good site not like that other site. 😉

beng135
Reply to  lee
April 5, 2022 2:58 am

You’re a good site, yes, such a good site, yes you are. Now roll over….

ATheoK
Reply to  lee
April 5, 2022 10:57 am

So much for improved accuracy.

Earthling2
April 4, 2022 10:44 pm

Very interesting. I hadn’t heard of the Nasa’s ER-2 aircraft much before, so looked it up, and seems very impressive to be flying at 70,000 feet doing scientific measurements from moonlight. I am all for collecting honest data, as long as it stays honest and doesn’t drive an agenda science, like CAGW.

https://www.nasa.gov/centers/armstrong/news/FactSheets/FS-046-DFRC.html

Steve Case
Reply to  Earthling2
April 5, 2022 12:14 am

The ER-2 looks like the U2 spy plane that Francis Gary Powers was flying when the Russians shot him down.

beng135
Reply to  Steve Case
April 5, 2022 2:59 am

Yeah, I think the design is pretty much the same except for some modern modifications. It’s still got the same fall-away wing supports for take off.

Last edited 1 month ago by beng135
Mike Sexton
Reply to  Steve Case
April 5, 2022 3:12 am

It’s also known as a TR-1

Richard Page
Reply to  Mike Sexton
April 5, 2022 9:40 am

It’s a modified and upgraded version of the U-2S which was an upgraded version of the TR-1A, itself a modified and upgraded 3rd batch version of the U-2. The U-2 has gone through several different versions since it was first introduced.

Mike Sexton
Reply to  Richard Page
April 5, 2022 12:19 pm

Yes I know I was just pointing out it is called by other designations

Graemethecat
Reply to  Richard Page
April 7, 2022 1:46 pm

Kelly Johnson would be amazed to know his U-2 would still be in service in 2022.

Old Man Winter
Reply to  Steve Case
April 5, 2022 3:57 am

This page lists the vast majority of US DoD aircraft. Click on an
aircraft designation for all the gory details:

https://military-history.fandom.com/wiki/List_of_U.S._DoD_aircraft_designations

If you click on 1962 United States Tri-Service aircraft designation system it will tell you what all the letters mean.

Wiki is pretty good for both civilian & military aircraft.

Old Man Winter
Reply to  Steve Case
April 5, 2022 4:08 am

Anthony managed to find a picture of a U-2 taking off from
Beale AFB, CA on Google Earth:

https://wattsupwiththat.com/2011/05/05/guess-the-image/

Gerald Hanner
Reply to  Steve Case
April 5, 2022 10:36 am

Quite a bit more advanced from the U-2 of the Powers era.

william Johnston
Reply to  Steve Case
April 5, 2022 11:39 am

It is. I saw the U-2 flying out of Turkey in 1958. Top secret plane. I know because the model airplane magazine in my possession at the time said so. Along with 3-view drawings and specs!

Gerald Hanner
Reply to  william Johnston
April 5, 2022 11:50 am

Yeah. It was from Turkey, or thereabouts, that Powers flew his fateful sortie. The Soviets finally refined their technique to reach high enough and guide their SA-2s close enough to the target to bring it down.

Reply to  Gerald Hanner
April 5, 2022 3:42 pm

The SR-71 was so fast that it once was targeted as it flew over the DMZ in Korea and the pilot was informed that a missile had been launched, he just tweaked the direction of the plane a few degrees and by the time the missile exploded , it was over 10 miles away

william Johnston
Reply to  Gerald Hanner
April 5, 2022 5:47 pm

Incirlik air base, Adana, Turkey

Gerry, England
Reply to  Earthling2
April 5, 2022 3:05 am

Once the data has been ‘corrected’ it will be fine….

beng135
Reply to  Earthling2
April 5, 2022 3:13 am

From the same site, the X-29 is pretty cool too.
https://www.nasa.gov/centers/armstrong/news/FactSheets/FS-008-DFRC.html

Carlo, Monte
Reply to  Earthling2
April 5, 2022 7:30 am

NASA also uses it for calibrating reference solar cells.

Clyde Spencer
Reply to  Carlo, Monte
April 5, 2022 9:29 am

And for flying AVIRIS (Airborne Visible-IR Imaging Spectrometer) for remote sensing, particularly minerals.

ATheoK
Reply to  Earthling2
April 5, 2022 10:59 am

Which departments of NASA are suddenly honest?

Richard Page
Reply to  ATheoK
April 5, 2022 12:39 pm

Depends. Which departments of NASA want to suddenly lose funding under the current administration?

AndyHce
April 4, 2022 11:03 pm

What would be the variances based on where the moon is in its orbit around the earth? There are regular, and possibly irregular changes for to a number of cycles from the normal monthly up to at least 18 years. These should change the amount of light receivable at any point at near earth distances.

The phases of the moon in it monthly cycle vary the amount of light the earth receives due to the amount of lighted moon earth can see.

There is also the yearly distance variance of the earth/moon system from the sun that changes the amount of light the moon receives from the sun, thus how much it can reflect towards earth.

There are solar cycles that vary the amount of light the earth/moon system receives within various frequency ranges,

Ben Vorlich
Reply to  AndyHce
April 5, 2022 1:17 am

According to the Internet – Metonic cycle, a period of 19 years in which there are 235 lunations, after which the Moon’s phases recur on the same days of the solar year. The cycle was discovered by Meton an Athenian astronomer. Computation from modern data shows that 235 lunations are 6,939 days, 16.5 hours; and 19 solar years, 6,939 days, 14.5 hours.

I’m not sure what the cycle is for the moon appearing at the same point (with same stars in the background sky) in the sky at the same phase is.

fretslider
Reply to  Ben Vorlich
April 5, 2022 3:42 am

Moon-letters are rune-letters, but you cannot see them,” said Elrond, “not when you look straight at them. They can only be seen when the moon shines behind them, and what is more, with the more cunning sort it must be a moon of the same shape and season as the day when they were written…..

Last edited 1 month ago by fretslider
Rocketscientist
Reply to  fretslider
April 5, 2022 8:48 am

We’ve been studying and fantasizing about out Moon since we became aware of it. Now there is much we know, but still little we understand.

F. Ross
April 4, 2022 11:39 pm

ER-2 aircraft… looks a lot like a U2 to me(?)

Ben Vorlich
Reply to  F. Ross
April 5, 2022 1:25 am

Research aircraft based on the U2, once the Russians had the technology to shoot down U2 aircraft the USA had an aircraft which wasn’t aable to perform its primary task but had useful scientific capabilities, so ER2 was the result.

Lockheed developed the SR71 Blackbird to perform the over flying spy missions. As far as I’m aware no SR71 has been shot down. Although modern hypersonic missile technology has probably made them vulnerable

rbabcock
Reply to  Ben Vorlich
April 5, 2022 3:07 am

SR-71’s were retired in 1998 by the USAF; 1999 by NASA. The newer ground to air missiles did come into play along with the fact they were just so darn expensive to fly and maintain. You have to admit it was one of the most iconic aircraft ever designed. It was also big. They are scattered around air museums.

Old Man Winter
Reply to  rbabcock
April 5, 2022 4:51 am

The SR-71 was the “Sierra Hotel” plane of my generation. I
was on “Cloud 9” when I actually could touch one at a
museum in Hutchinson, KS. Being that close to it inside a
building made it look smaller than I remembered it to be.

Ron Long
Reply to  Ben Vorlich
April 5, 2022 3:50 am

Ben, in 1989, while I was examining a nearby Yuba Dredge, extracting placer gold, I stopped at the north end of the Beale Air Force Base and watched a SR-71 Blackbird take off. Although we were around a kilometer away, the roar and air vibration at the start of the take-off roll was incredible.

Old Man Winter
Reply to  Ben Vorlich
April 5, 2022 4:39 am

The USAF had both the U-2 & SR-71 @ Mildenhall AB in England.
All of their activities were scheduled around the times when
Soviet satellites were overhead. Our planes were parked next to
their hangars so often times we’d see someone with binoculars
outside the base perimeter chain-linked fence looking at the
hangars. They were full-fledged Commies who would record tail #s
& take-off times which would eventually get relayed to the Soviets to
give them a heads-up on when to look for them, as they’d regularly
recon the Iron Curtain, among other places.

The U-2 only has landing gear under the fuselage & a small wheel
under each wing, which they eject after take-off. So when they
land, they have a chase car to help the pilot land, after which they
re-install those wheels so they can taxi.

https://www.warhistoryonline.com/military-vehicle-news/land-the-u-2-dragon-lady.html?msie=1

Yirgach
Reply to  F. Ross
April 6, 2022 1:02 pm

A father of a good friend of mine (now both off-planet) was a member of the Lockheed Martin Skunk Works team which built and tested the U2. He also knew Powers personally. After he was released Powers told him that the top brass were po-ed when he didn’t suicide after being captured.

Steve Case
April 5, 2022 12:05 am

“The Moon is extremely stable and not influenced by factors on Earth like climate to any large degree. It becomes a very good calibration reference…
 
And from the IPCC’s AR4 Chapter 2 Page 210
the … GWP index, based on the time-integrated global mean RF of a pulse emission of 1 kg of some compound (i) relative to that of 1 kg of the reference gas CO2…
______________________________________________________________

Yes we need stable references which is why the IPCC uses CO2 as a the reference gas for their Global Warming Potential (GWP) calculations. [/sarc]

If you follow the IPCC link above they go on to say that the atmospheric abundance of the reference gas CO2 is in the denominator of their formula.

And as you know, the abundance of CO2 is in Parts Per Million and is NOT stable. But that’s what the IPCC has to do if they want to claim that methane is 86 times more powerful than CO2.

In other words, the GWP increases along with the increase in CO2 as follows in the first five IPCC reports: 63, 56, 62, 72, 86.

marty
April 5, 2022 2:43 am

This ER-2 airplane reminds me of the U-2 airplane… :-))

marty
April 5, 2022 2:53 am

“The results will compliment ground-based sites” Do those ground-based sites include military sites?

observa
April 5, 2022 2:54 am

And here was me thinking their data and science were settled. Now where would I have got that silly notion from?

H.R.
Reply to  observa
April 5, 2022 6:39 am

‘The Science’ is settled. The data? Not so much.

rbabcock
April 5, 2022 3:09 am

I’m glad they are getting the measuring satellites accuracy better. Just in time for the coming little ice age.

fretslider
April 5, 2022 3:49 am

So, what’s this effort’s carbon footprint, then?

And how does Nasa offset it?

Nasa has been working on electric planes for the past decade, grappling with laws of physics that haven’t dogged the mainstream adoption of electric cars. Currently, to power a 737-size jet with electricity would require a battery the size of the plane itself. “

https://www.theguardian.com/us-news/2021/may/18/electric-planes-nasa-carbon-emissions

If it’s really as bad as they say – or even worse – how do they sleep at night?

Peta of Newark
April 5, 2022 3:59 am

Is someone getting carried away with themselves….
Quote:This light includes visible light, which humans see, as well as invisible ultraviolet and infrared wavelengths, and everything in between.

Hang on..
There is Visible Light, hemmed in by longer wavelength Infra Red and shorter wavelength Ultraviolet

So where is this ‘everything in between‘?
There is no ‘in between

As I was taught, Moon is effectively black – with Albedo of ~0.11
Reflected light is very low, but for a Sputnik that’s no real problem.

The only real reason why us human types see the Moon is because it’s Phosphorescent. It doesn’t hardly reflect anything that we could see.
As a kid I was told that Moon emits much more visible light than it reflects
Maybe that is the 1% allowance they give themselves?

(Except during Blood Moon eclipses – when it turns red in colour because of sunlight that’s been /processed/filtered by Earth’s atmosphere)

That Phosphorescence is created by and depends on Ultraviolet coming off El Sol. My guess is that’s why Moon is so fascinating, it is such an odd, unnatural and cold sort of colour.

Sol varies its UV output like a candle in the wind. (Has it a lot to do with sunspots – do they make a lot of UV?)
We know solar UV varies a lot in amplitude and on all sorts of timescales – by the amount of Stratospheric Ozone there is. The size of the Antarctic Ozone Hole is a neat proxy because solar UV is what makes all the Ozone in the first place.
(Isn’t that right NASA – so why do you never tell anyone – especially while raving about CFCs destroying said Ozone?)

How does their telescope account for that – is it ‘blind’ to the Phosphorescence coming off the Moon. How do they know which light is reflected and which is emitted?

(That last bit goes to The Very Heart of the GHGE doesn’t it just – what exactly does happen to the energy absorbed by greenhouse gases – especially when the chief villain of the peace has zero emissivity.
Again – isn’t that right NASA and why your own OCO Sputnik doesn’t even bother looking for CO2 ‘re-emitted in all directions‘ energy – there isn’t any for it to see. John Tyndall too)

In fact, OCO Sputnik does demonstrate/prove atmospheric warming caused by extra CO2 (NOT warming of the surface soil, dirt, plants etc)
If the surface is warming, something else is going on.

OCO looks for solar energy at temps of 400 and 800 Celsius that have been absorbed by CO2 – temperatures/wavelengths which would have a very potent heating effect. This being effectively what Tyndall recorded.

iow: OCO records the amount of (extra) incoming solar energy that the extra CO2 is absorbing – at altitudes perfectly suited for Spencer’s Sputniks to measure the temperature changes.

which thimble is the pea now under

Last edited 1 month ago by Peta of Newark
Duane
Reply to  Peta of Newark
April 5, 2022 4:50 am

Utter balderdash. Nearly all of the visible moonlight is reflected sunlight, there is no such thing as “phosphorescence of the moon”. Phosphorescence is a process involving a surface absorbing incoming light, and shortly thereafter re-emitting light at a longer wavelength. So if phosphorescence were the predominant direct source of moonlight on earth, instead of the white light that is emitted by the sun, the moonlight would appear greenish or even reddish.

Also the moon isn’t black – it is gray. If it were black it would not reflect any sunlight. The fact that it is gray is why the moon reflects 12% of incoming sunlight. Photographs taken of the moon from orbit and on the surface clearly show its gray surface color due to the composition of its rocks and dust.

By the way, when I read your comment and then googled “moon phosphorescence”, the first hit that came up was a post by the Flat Earth Society. ‘Nuff said!

Last edited 1 month ago by Duane
Bob boder
Reply to  Duane
April 5, 2022 5:11 am

FES lol. Petra is smoking something really good me thinks.

Alexy Scherbakoff
Reply to  Bob boder
April 5, 2022 5:26 am

Either red drink or electrolytes.
Hilarious.

Last edited 1 month ago by Alexy Scherbakoff
Clyde Spencer
Reply to  Duane
April 5, 2022 9:47 am

Moon rocks are rich in feldspars. If they fluoresce at all, they typically fluoresce pink. Phosphorescence is a delayed response after UV stimulation is ceased.

The article doesn’t make it clear whether NASA is measuring the moon surface illuminated by the sun, or light reflected by Earth, so-called Earthshine. If the surface of the moon were fluorescing to any significant degree, the solar-illuminated limb would appear a different color than the Earth-illuminated portion because there would be almost no UV reflected from Earth.

Peta has outdone himself.

fretslider
Reply to  Peta of Newark
April 5, 2022 5:07 am

As a kid I was told that Moon emits much more visible light than it reflects”

The question has to be, do you believe it?

M Courtney
Reply to  fretslider
April 5, 2022 6:00 am

Why would anyone believe it?
Most things reflect light. Why not the moon?
Most things do not get excited and emit light in the visual spectrum.
It’s just so improbable.
Has anyone seen the phosphorescent glow from the dark side of the moon shimmering round the new moon?
No.

Rocketscientist
Reply to  Peta of Newark
April 5, 2022 9:07 am

Lunar phosphorescence, um… NO!

But, because the moon as no atmosphere to reflect away solar radiation all of it does reach the surface. Lunar rocks and regolith (its not soil) can be distinguished from terrestrial rocks by their radiation signatures as they are slightly more radioactive. However, this is a testament to our ability to detect minute amounts of radiation not because they present any greater threat.

The big reason we use the moon for calibration is that it is tidally locked to earth in that it ALWAYS shows the same face to Earth. The amount of radiation that face gets varies with the moon’s phases. There is a much more detailed description of lunar periodicity mentioned below.

Peter Fraser
Reply to  Rocketscientist
April 5, 2022 12:14 pm

Many people believe that foodstuffs left overnight in bright moonlight are detrimentally effected including milk going sour and meat spoiling. Sometimes a grain of truth in old wives tales.

David Dibbell
April 5, 2022 4:25 am

“NASA has more than 20 Earth-observing satellites that give researchers a global perspective on the interconnected Earth system.”

I appreciate that part of NASA is still working on sensing and imaging. If the climate researchers would just honestly admit what the resulting products are telling us, we could get past this illusion that CO2 emissions must be driving the climate outcome.

Here is an example – Band 2, the “red” visible channel, from the GOES-16 geostationary satellite’s imager, for the “CONUS” area (continental US). This animation is 240 images at 5-minute intervals, so 20 hours worth. The resolution is 0.5 km. It takes a while to load, but it’s worth it to appreciate the variability of reflected sunlight from clouds and the overall motion. Some images may be skipped, and of course some are in the dark. Let it load, and watch a few times. It gives the most recent 240 images from whenever you click on it.

https://www.star.nesdis.noaa.gov/GOES/conus_band.php?sat=G16&band=02&length=240&dim=1

How can the low-resolution, step-iterated climate models ever compute the albedo of a grid cell, let alone the whole planet, well enough to quantify the absorbed solar energy at each time-step during daylight?

Sooner or later, the space-based images will be very helpful for folks to get past the GHG warming scare. So more power to those at NASA that are doing this.

Last edited 1 month ago by David Dibbell
rbabcock
Reply to  David Dibbell
April 5, 2022 6:52 am

The College of DuPage Illinois has a great dashboard. GOES-16/17 plus the GFS etc models under Weather Data. Pick your area and bookmark it for a quick look.
https://weather.cod.edu/satrad/?parms=subregional-Carolinas-truecolor-24-1-100-1&checked=map&colorbar=undefined.cod.edu/satrad/?parms=subregional-Carolinas-02-12-1-100

David Dibbell
Reply to  rbabcock
April 5, 2022 7:10 am

Very cool. Thanks.

Duane
April 5, 2022 4:33 am

But this study begs the question, since the purpose of this data collection is to fine tune the data collection of earth-observing satellites, why don’t those satellites carry their own moonlight sensors to self-calibrate? After all that would be a more precise calibration since it would have zero effect from atmospheric light scattering.

MarkW
Reply to  Duane
April 5, 2022 9:03 am

Rather than have a separate sensor, I would think they would want to point their primary sensor at the moon for calibration. However before you can calibrate you have to know what your sensors should be reading. For that you need an official standard. Which is what they are trying to gather here.

Clyde Spencer
Reply to  MarkW
April 5, 2022 9:55 am

I’m not sure why they are using the ER-2 to measure the moon. The GOES geostationary satellites use the moon to calibrate their imagers. And, the International Space Station has a spectrometer (OCO-3) that could probably be used.

Rocketscientist
Reply to  Duane
April 5, 2022 9:09 am

Probably would add a lot of cost. How much did NASA spend for just this one?

Gunga Din
Reply to  Duane
April 5, 2022 3:27 pm

Mr. Layman here. I had the same thought.
Perhaps they are looking for a standard for satellites that are already in orbit and/or are about to be launched that don’t already have a “Moon gauge” installed or designed into the system?
Just a thought.

Randle Dewees
April 5, 2022 6:43 am

I wonder about Abby’s education background – lots of analogies to music. But not once did she use the word “radiometric”. I bet she heard that word many times in her interviews with Kevin Turpie.

“the light to the spectrometer, which is an instrument that measures variances of light waves.”

I would bet she meant to say “spectrophotometer”. As for “variances of light waves”, really, I have no comment.

Radiometric accuracy is no joke. I design and field radiometers (transmissometers) for rough and tumble dynamic military range testing of high energy lasers (HEL). The formal expectation for accuracy is +- 10%! That is hard to achieve outside of static lab like settings. I respect what NASA, NIST, and Turpie are doing.

Carlo, Monte
Reply to  Randle Dewees
April 5, 2022 7:28 am

The article was certainly the work of a tech writer, who have the task of translating real technical writing into something they think the general public can understand. Typically they lack the technical skills needed to understand the source documents so they have to pester the original authors, who quickly get annoyed and just want them to go away.

“Spectrometer” is okay, but the real term is “spectroradiometer”, which measures spectral irradiance. This differentiates them from spectrophotometers which measure reflectance and transmittance. Both by necessity contain spectrometers. “Variances of light waves” is likely tech writer-mush for spectroradiometer.

Radiometric accuracy is no joke.

Yes! This <1% number is way optimistic.

Randle Dewees
Reply to  Carlo, Monte
April 5, 2022 7:46 am

Yes, agree on the spectroradiometer as the better term. In my youth I did use commercial spectrophotometers a lot for transmission measurements of IR materials we (Exotic Materials Inc) were making. Since I now work only one wavelength, with a beacon at 1.06um, I’m just tranmissometering away.

Yes! This <1% number is way optimistic.” but obtainable I would think if the PI is subtle and diligent.

Carlo, Monte
Reply to  Randle Dewees
April 5, 2022 12:07 pm

Low radiometric uncertainty is possible with single wavelengths, i.e. lasers, but spanning a significant wavelength range is a completely different animal.

Tim Gorman
Reply to  Carlo, Monte
April 5, 2022 3:56 pm

I know radio waves bounced off the moon suffer polarization effects from the uneven surface of the moon. I would expect the same for IR and optical as well. How are these impacts accounted for at the sensor?

Carlo, Monte
Reply to  Tim Gorman
April 5, 2022 4:31 pm

With the integrating sphere, which homogenizes the light just before it enters the entrance slits of the spectrometer. After all the internal reflections inside the sphere, the light is essentially randomly polarized.

Tim Gorman
Reply to  Carlo, Monte
April 6, 2022 6:03 am

Do the satellites do the same thing using the same device? If not then how can one be used as a calibration standard?

Carlo, Monte
Reply to  Tim Gorman
April 6, 2022 12:44 pm

I don’t know, probably would have to study the real reports rather than the tech writer’s interpretation. The impression I got was the purpose is to measure lunar albedo, if so the measured lunar spectral irradiance would be ratioed with the known solar extraterrestrial spectrum. Then the albedo would function as the calibration curve, but I could be wrong.

Tim Gorman
Reply to  Carlo, Monte
April 6, 2022 4:04 pm

So the uncertainty would be how accurately we know the involved albedos?

Carlo, Monte
Reply to  Tim Gorman
April 7, 2022 2:22 pm

I think this is the gist, but again, I could well be wrong.

Clyde Spencer
Reply to  Randle Dewees
April 5, 2022 9:58 am

I respect what NASA, NIST, and Turpie are doing.

Assuming that they have achieved the claimed accuracy. It is my understanding that +/- 3% is very good work in photometry.

Carlo, Monte
Reply to  Clyde Spencer
April 5, 2022 12:08 pm

Correct, and the value varies with wavelength. It is significantly higher in the UV.

Carlo, Monte
April 5, 2022 7:13 am

air-LUSI measurements are accurate with less than 1% uncertainty

Spectral irradiance measurements on the ground cannot be performed with less than 1% uncertainty—the biggest problem is the reference standard lamps provided by NIST.

How do they know the transmittance of the necessary window(s) to this level?

Joao Martins
April 5, 2022 12:07 pm

The Moon is extremely stable and not influenced by factors on Earth like climate to any large degree

AT LAST !!!

Something that climate change does not do !!!!

Robert of Texas
Reply to  Joao Martins
April 5, 2022 5:50 pm

Well, this just in… Some places are wetter so more clouds meaning more light reflected. Some places are darker due to reduction of snow and ice, so climate (magic) change is causing the Moon to change its reflected intensity. This is causing cicadas to mass migrate across Egypt and is leading to one of the signs of the End-of-the-World. We only have until 2031 according to our self-designated prophet AOC.

Only Green Energy can save us, as the color green seems to pacify the cicadas.

;-D

Robert of Texas
April 5, 2022 2:12 pm

If the “calibration” is about 99% accurate than how can they report results in 1/10th and even 1/100th degrees? The error should be additive (or multiplicative), so added into the other error margins of instruments, atmospheric turbulence, orbit variance, etc.

Tim Gorman
Reply to  Robert of Texas
April 5, 2022 4:23 pm

They can’t discern results in the tenths and hundredths. They either confuse precision with uncertainty or they just totally ignore uncertainty all together. Even worse they use standard deviation of sample means as the uncertainty of the mean. They are not the same thing. You can get a very small standard deviation of the sample means while systemic bias in the measurements is a large value. In this case it doesn’t matter how small the standard deviation of the sample means is, you’ll never get an accurate value for the mean.

Ruleo
April 6, 2022 7:44 pm

Yeah but the conventional wisdom that the Earth’s albedo is as high as the Moon’s still remains (it’s not, Earth is dark- Himawari).

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