Australian Politics Forum - Why satellites cannot measure sea level..??

Ajax

Gold Member

Offline

CO2 has never controlled
temperature on Earth

Posts: 10975
Australia
Gender: male

Re: Why satellites cannot measure sea level..??
Reply #75 - Sep 21^st, 2013 at 2:12pm

muso wrote on Sep 21^st, 2013 at 11:21am:

Ajax wrote on Sep 21^st, 2013 at 10:28am:

I have given you links as to how and why......!!!!

Denying them means you must know more......!!!!

But you're only one person claiming this or that, and you're probably not an expert.

So I know who I believe.

This is a good indication of why you shouldn't be taken seriously. You are totally out of your depth but refuse to acknowledge the fact.

LOL...and this is why we shouldn't take you seriously...??

http://www.altimetry.info/html/alti/principle/welcome_en.html

http://www.ips.gov.au/Educational/1/3/2

Back to top

1. There has never been a more serious assault on our standard of living than Anthropogenic Global Warming..Ajax
2. "One hour of freedom is worth more than 40 years of slavery & prison" Regas Feraeos

IP Logged

muso

Gold Member

Offline

Posts: 13151
Gladstone, Queensland
Gender: male

Re: Why satellites cannot measure sea level..??
Reply #76 - Sep 21^st, 2013 at 2:38pm

Anyway, regardless of your very inventive concepts of perturbations by energetic protons on radio wave frequencies, I have already posted the accuracy and precision data for Jason 2 and the Poseidon-3 radar altimeter, and the methodology for the altimetry calculation. Unlike your guesses, these came directly from the specifications - from the CNES engineers who built the equipment. This was confirmed in a period of testing following orbital insertion.

What was the precision of the measurement again? (I did provide you with that information)

You don't have to rely on nonsense from Willie Soon.

Back to top

1523 people like this. The remaining 7,134,765,234 do not

IP Logged

Ajax Gold Member Offline CO2 has never controlled temperature on Earth Posts: 10975 Australia Gender:	Re: Why satellites cannot measure sea level..?? Reply #77 - Sep 21^st, 2013 at 2:44pm Quote: The absolute accuracy is +/- 2.5cm, but the precision (stability) is better than 1mm. Please explain this to a layman...??? In layman's term please......!!!!!
Back to top	1. There has never been a more serious assault on our standard of living than Anthropogenic Global Warming..Ajax 2. "One hour of freedom is worth more than 40 years of slavery & prison" Regas Feraeos IP Logged

muso

Gold Member

Offline

Posts: 13151
Gladstone, Queensland
Gender: male

Re: Why satellites cannot measure sea level..??
Reply #78 - Sep 21^st, 2013 at 3:40pm

What it means is that the exact distance may be out by 25mm, but the precision is to the nearest mm. In other words, if the distance is x, then it can detect a change in that reading from year to year to the nearest mm. When you have a systematic error, the precision can be improved by taking a larger sample size. So, the different agencies report slightly different precisions.

GMSL Rates
CU: 3.2 ± 0.4 mm/yr
AVISO: 3.2 ± 0.6 mm/yr
CSIRO: 3.2 ± 0.4 mm/yr
NOAA: 3.2 ± 0.4 mm/yr (w/ GIA)

I'm sorry if I haven't been helpful in explaining this, but you were adopting a brick wall position. To take an example, let's say you have a 10 metre measuring pole that is monitoring the subsidence of a Highset building (Say a Queenslander). That ruler may have an accuracy of +/- 10mm, but the precision of the measurement might be +/- 1mm. So you can estimate the height to the ground floor with an accuracy of 10mm, but the precision of the measurement is to the nearest mm. So you can tell if the building is sinking by say 1mm per month, but you can't tell the height to the ground as accurately as that.

Please tell me that you understand this.

Back to top

1523 people like this. The remaining 7,134,765,234 do not

IP Logged

muso

Gold Member

Offline

Posts: 13151
Gladstone, Queensland
Gender: male

Re: Why satellites cannot measure sea level..??
Reply #79 - Sep 21^st, 2013 at 3:57pm

By the way, the factor that changes when electromagnetic radiation passes through a varying medium is the speed. Air has a refractive index of about 1.0002. So the speed of light and other electromagnetic radiation is around 90km/ second slower in air compared to a vacuum.

The pathway itself doesn't change the frequency or wavelength. What does change the frequency of the received radiation is the motion of the satellite itself. That's called the Doppler effect, and that's taken into account.

You must have come across the terms red shift or blue shift.

Back to top

1523 people like this. The remaining 7,134,765,234 do not

IP Logged

Ajax

Gold Member

Offline

CO2 has never controlled
temperature on Earth

Posts: 10975
Australia
Gender: male

Re: Why satellites cannot measure sea level..??
Reply #80 - Sep 22^nd, 2013 at 10:34am

muso wrote on Sep 21^st, 2013 at 3:40pm:

What it means is that the exact distance may be out by 25mm, but the precision is to the nearest mm. In other words, if the distance is x, then it can detect a change in that reading from year to year to the nearest mm. When you have a systematic error, the precision can be improved by taking a larger sample size. So, the different agencies report slightly different precisions.

GMSL Rates
CU: 3.2 ± 0.4 mm/yr
AVISO: 3.2 ± 0.6 mm/yr
CSIRO: 3.2 ± 0.4 mm/yr
NOAA: 3.2 ± 0.4 mm/yr (w/ GIA)

I'm sorry if I haven't been helpful in explaining this, but you were adopting a brick wall position. To take an example, let's say you have a 10 metre measuring pole that is monitoring the subsidence of a Highset building (Say a Queenslander). That ruler may have an accuracy of +/- 10mm, but the precision of the measurement might be +/- 1mm. So you can estimate the height to the ground floor with an accuracy of 10mm, but the precision of the measurement is to the nearest mm. So you can tell if the building is sinking by say 1mm per month, but you can't tell the height to the ground as accurately as that.

Please tell me that you understand this.

I'm not being a smart asre here but genuine.

The statements in your post about accuracy can they be for the ideal condition....???

Where nothing interferes with the signal.......????

Because when I look up the accuracy of altimeters, most of the information says that they can only read to an accuracy of about one to two centimetres due to interference factors.

Have a squiz here.

http://www.altimetry.info/html/alti/principle/waveform/welcome_en.html

http://www.altimetry.info/html/alti/dataflow/processing/pod/welcome_en.html

http://www.altimetry.info/html/appli/hydro/welcome_en.html

Personally I find it hard to believe that they could measure with an accuracy of one millimetre.

Especially when they say that they can track the satellite position in space to within a few centimetres.

And

The frequency is affected by the atmosphere to some extent.

I could believe 10mm to 20mm but 1mm I have a hard time believing that.

That's just me I suppose, I always doubt things until it can be proven.

Back to top

1. There has never been a more serious assault on our standard of living than Anthropogenic Global Warming..Ajax
2. "One hour of freedom is worth more than 40 years of slavery & prison" Regas Feraeos

IP Logged

muso

Gold Member

Offline

Posts: 13151
Gladstone, Queensland
Gender: male

Re: Why satellites cannot measure sea level..??
Reply #81 - Sep 22^nd, 2013 at 10:42am

Ajax, read my last post again, and particularly the example on the house subsidence. Do you understand the difference between accuracy and precision? I don't think you've twigged yet.

After they launched Jason 2, there was a period where they compared data against Jason 1. The measurements were adjusted for the systematic error over that period.

Read the post over. It will twig eventually.

Quote:

The statements in your post about accuracy can they be for the ideal condition....???

Where nothing interferes with the signal.......????

(First of all precision, not accuracy is important here. )

No. During a severe solar storm, there are no measurements. Moisture in the air path is corrected for. There are no ideal conditions.

Let me know when you understand so we can move on.

Back to top

1523 people like this. The remaining 7,134,765,234 do not

IP Logged

Ajax

Gold Member

Offline

CO2 has never controlled
temperature on Earth

Posts: 10975
Australia
Gender: male

Re: Why satellites cannot measure sea level..??
Reply #82 - Sep 22^nd, 2013 at 11:02am

I think we are going to have to agree to disagree on this one.

I've taken in what you've said and what articles that I have found say.

I'm still not convinced that satellites can read with an accuracy of 1mm.

Quote:

1.7. Coastal applications

Many current studies are attempting to enhance the quality of altimetry data close to the coasts. New processing methods and applications can then be developed for littoral and shallow-water regions, some of the most fragile and important areas of the oceans.

The shortage of altimetry data near the coasts (or their inferior quality) is due to several factors:
- the technique itself, since the radar echoes reflected off water, and off a combination of water and land are not identical, and basically only the former undergo processing by the ground segments. Other altimetry satellite measurements also suffer from the same problem, such as those from the radiometer (at a distance of about 50 km from the coast)
- - the fact that the basic distributed data (GDR) are mainly average over one second, thus covering about 7 km on the ground (data averaged over 1/20 s do exist, however).
- the computation of some corrections. Tides, in particular, are much more complex near the shores than in the open sea, and require a highly precise knowledge of the coastal geography to be accurately computed. Moreover, rapid variations ("high frequency") must be taken into account in those areas (for the tides as well as for the atmospheric pressure). Wet tropospheric corrections, computed from radiometer measurements are also less precise, or even missing, near the coasts.

http://www.altimetry.info/html/appli/coastal/welcome_en.html

Back to top

1. There has never been a more serious assault on our standard of living than Anthropogenic Global Warming..Ajax
2. "One hour of freedom is worth more than 40 years of slavery & prison" Regas Feraeos

IP Logged

muso

Gold Member

Offline

Posts: 13151
Gladstone, Queensland
Gender: male

Re: Why satellites cannot measure sea level..??
Reply #83 - Sep 22^nd, 2013 at 11:30am

Ajax wrote on Sep 22^nd, 2013 at 11:02am:

I think we are going to have to agree to disagree on this one.

I've taken in what you've said and what articles that I have found say.

I'm still not convinced that satellites can read with an accuracy of 1mm.

Not accuracy, precision! a precision of 1mm. Read my post again. An accuracy of 25mm and a precision of 1mm.

Am I not explaining this well enough?

Back to top

1523 people like this. The remaining 7,134,765,234 do not

IP Logged

Ajax

Gold Member

Offline

CO2 has never controlled
temperature on Earth

Posts: 10975
Australia
Gender: male

Re: Why satellites cannot measure sea level..??
Reply #84 - Sep 22^nd, 2013 at 11:39am

muso wrote on Sep 22^nd, 2013 at 11:30am:

Ajax wrote on Sep 22^nd, 2013 at 11:02am:

I think we are going to have to agree to disagree on this one.

I've taken in what you've said and what articles that I have found say.

I'm still not convinced that satellites can read with an accuracy of 1mm.

Not accuracy, precision! a precision of 1mm. Read my post again. An accuracy of 25mm and a precision of 1mm.

Am I not explaining this well enough?

Are you saying that the accuracy can be 25mm plus or minus a millimetre......????????

In which case it would be impossible to measure the 7mm drop in sea levels in the year 2011.....!!!!

Back to top

1. There has never been a more serious assault on our standard of living than Anthropogenic Global Warming..Ajax
2. "One hour of freedom is worth more than 40 years of slavery & prison" Regas Feraeos

IP Logged

muso

Gold Member

Offline

Posts: 13151
Gladstone, Queensland
Gender: male

Re: Why satellites cannot measure sea level..??
Reply #85 - Sep 22^nd, 2013 at 12:24pm

No. You don't understand precision. Let me think about how to explain this to you best. Here, I'll let somebody else explain.

http://celebrating200years.noaa.gov/magazine/tct/tct_side1.html

Quote:

To illustrate the distinction between terms using a surveying example, imagine surveyors very carefully measuring the distance between two survey points about 30 meters (approximately 100 feet) apart 10 times with a measuring tape. All 10 of the results agree with each other to within two millimeters (less than one-tenth of an inch). These would be very precise measurements. However, suppose the tape they used was too long by 10 millimeters. Then the measurements, even though very precise, would not be accurate. Other factors that could affect the accuracy or precision of tape measurements include: incorrect spacing of the marks on the tape, use of the tape at a temperature different from the temperature at which it was calibrated, and use of the tape without the correct tension to control the amount of sag in the tape.

If you were conducting a study on the gradual increase in Global Ocean Level, which would be most useful to you? Accuracy or precision?

What about if your study is on the absolute sea level. Accuracy or precision?

Back to top

« Last Edit: Sep 22^nd, 2013 at 12:35pm by muso »

1523 people like this. The remaining 7,134,765,234 do not

IP Logged

Ajax

Gold Member

Offline

CO2 has never controlled
temperature on Earth

Posts: 10975
Australia
Gender: male

Re: Why satellites cannot measure sea level..??
Reply #86 - Sep 24^th, 2013 at 5:43pm

muso wrote on Sep 22^nd, 2013 at 12:24pm:

If you were conducting a study on the gradual increase in Global Ocean Level, which would be most useful to you? Accuracy or precision?

What about if your study is on the absolute sea level. Accuracy or precision?

Both would be necessary otherwise you're claim would be subjected to criticism....!!

This will depend upon the instruments you're using and how your measurements stack up against other methods that measure the same thing.

So let me ask you a question.......???????

The information you posted says that the accuracy can be within plus or minus 25mm.

Making the overall drift or error margin 50mm....!!!!!

So then if all your measurements taken with the satellite fall within 50mm range or mark.

Are these deemed to be precise...............???????

Precision is 50mm +- 1mm.

Back to top

1. There has never been a more serious assault on our standard of living than Anthropogenic Global Warming..Ajax
2. "One hour of freedom is worth more than 40 years of slavery & prison" Regas Feraeos

IP Logged

muso Gold Member Offline Posts: 13151 Gladstone, Queensland Gender:	Re: Why satellites cannot measure sea level..?? Reply #87 - Sep 24^th, 2013 at 6:58pm Off-Topic replies have been moved to this Topic.
Back to top	1523 people like this. The remaining 7,134,765,234 do not IP Logged

muso

Gold Member

Offline

Posts: 13151
Gladstone, Queensland
Gender: male

Re: Why satellites cannot measure sea level..??
Reply #88 - Sep 24^th, 2013 at 7:10pm

Ajax wrote on Sep 24^th, 2013 at 5:43pm:

muso wrote on Sep 22^nd, 2013 at 12:24pm:

If you were conducting a study on the gradual increase in Global Ocean Level, which would be most useful to you? Accuracy or precision?

What about if your study is on the absolute sea level. Accuracy or precision?

Both would be necessary otherwise you're claim would be subjected to criticism....!!

This will depend upon the instruments you're using and how your measurements stack up against other methods that measure the same thing.

So then if all your measurements taken with the satellite fall within 50mm range or mark.

Are these deemed to be precise...............???????

Precision is 50mm +- 1mm.

You still haven't got it.

Quote:

Quote:

If you were conducting a study on the gradual increase in Global Ocean Level, which would be most useful to you? Accuracy or precision?

(Precision)

What about if your study is on the absolute sea level. Accuracy or precision?

Accuracy

Both would be necessary otherwise you're claim would be subjected to criticism....!!

I gave you the answers. Have a look at them and see if you understand.

Quote:

So let me ask you a question.......???????

The information you posted says that the accuracy can be within plus or minus 25mm.

Making the overall drift or error margin 50mm....!!!!!

Error margin (accuracy of absolute distance) and drift are totally different things.

The drift is less than 1mm. I already gave you that. The stability is better than 1mm. That's the precision.

Now I'll attempt to explain again. We don't know the distance accurately, but the measurement that we get is stable to 1mm. So it doesn't matter the fact that the distance may have a systematic error of +/- 25mm, what matters is that we can tell the difference between readings with a precision better than 1mm. In fact it's 0.4mm or 0.6mm depending on the agency.

Ajax, Please read this example again

Quote:

To illustrate the distinction between terms using a surveying example, imagine surveyors very carefully measuring the distance between two survey points about 30 meters (approximately 100 feet) apart 10 times with a measuring tape. All 10 of the results agree with each other to within two millimeters (less than one-tenth of an inch). These would be very precise measurements. However, suppose the tape they used was too long by 10 millimeters. Then the measurements, even though very precise, would not be accurate. Other factors that could affect the accuracy or precision of tape measurements include: incorrect spacing of the marks on the tape, use of the tape at a temperature different from the temperature at which it was calibrated, and use of the tape without the correct tension to control the amount of sag in the tape.

Let me know when you get it. I'm sure that you'll kick yourself when you finally do.

Back to top

« Last Edit: Sep 24^th, 2013 at 7:16pm by muso »

1523 people like this. The remaining 7,134,765,234 do not

IP Logged

muso

Gold Member

Offline

Posts: 13151
Gladstone, Queensland
Gender: male

Re: Why satellites cannot measure sea level..??
Reply #89 - Sep 25^th, 2013 at 8:04am

If you're measuring an altitude, the actual figure you get may be off by =/- 25mm. OK?

However the stability or precision of that reading is better than 1mm.

Let's take some hypothetical readings in mm. The dotted lines represent the other digits of a very large number. In each case, that number is the same. I know that this is not literally correct, but I'm just trying to convey the concept of precision.

..................156.7 mm
..................156.3 mm
..................156.5 mm
..................156.2 mm
..................156.5 mm
..................156.4 mm
..................156.6 mm
..................156.7 mm
..................156.3 mm
..................156.5 mm

OK, you can see that it's a stable reading, but the absolute value could be out as much as 25mm either side.

If you are measuring the change in value from year to year, then that absolute value doesn't matter. You can still measure the change from year to year with a confidence of better than 1mm.

That's what's meant by precision.

Back to top

« Last Edit: Sep 25^th, 2013 at 8:10am by muso »

1523 people like this. The remaining 7,134,765,234 do not

IP Logged