(Very) Preliminary Quality Assessment of Stratospheric AMSU Channels

(Channels 9 – 14)

Carl Mears

Remote Sensing Systems

AMSU and SSU Weighting Functions

AMSU 9

AMSU 10

AMSU 11

AMSU 12

AMSU 13

SSU 15x

SSU 25

SSU 26SSU 27

Some Results from the Troposphere and Lower Stratosphere

Problems with AMSUMid-Troposphere

Funny behavior for near-limb views

Problems with AMSU(Near Tropopause)

Other channels at least as bad!

Some indication that target factor could be FOV dependent!

Problems with AMSU

How do we figure out which AMSU instrument is bad (or at least, less bad)

• Radiosondes probably not accurate enough

• Time period too short for water vapor to help

• NOAA-16 farther way from NOAA-14 MSU (but this is an old instrument)

Solution: Figure out which AMSU has a more consistent dataset by looking at all channels (and nadir vs limb views)

Probable vertical structure of trends

Trend

Height

Tropopause

Trends – NOAA-15 and NOAA-16Tropical Oceans, 30S to 30N

NOAA-15: Fairly consistent

except for Channel 6.

NOAA-16: All channels inconsistent except for (maybe) channel 4.

Trends – NOAA-15 and NOAA-16 Tropical Oceans, 30S to 30N, 2002-2006

NOAA-15: Fairly consistent

except for Channel 6.

NOAA-16: All channels inconsistent except for (maybe) channel 4.

Conclusion: NOAA-16 more likely to be the problem – NOAA-16 is removed.

Now, the Stratosphere

• Basis strategy – apply the same analysis to the stratospheric channels to see if NOAA-16 has problems for these channels too.

• Very preliminary, since we have not performed any diurnal adjustment.

• Difficult to evaluate channels 11 and 14 due to short (or zero) overlap

Trends, 2002-2006, K/decade60S to 60N

Trends broadly consistent for all stratospheric channels

Nadir-limb difference seems too large

- related to diurnal drift?

Channel 10 Time Series

Tem

pera

ture

Tem

pera

ture

Ano

mal

yN

OA

A-1

6 –

NO

AA

15

For Channel 10, everything is fairly well behaved.

Channel 12 Time Series

Tem

pera

ture

Tem

pera

ture

Ano

mal

yN

OA

A-1

6 –

NO

AA

15

For Channel 12, descending node shows significant drift.

Adjusting for drifts in measurement time

NOAA satellites drift in local measurement time

If uncorrected, these would lead to spurious long-term

signals in the dataset.

NOAA-15

NOAA-16

NOAA-16 minus NOAA-15 differencesby field of view.

Drift in descending node strongly dependent on field of view.

At least part of this is due to drift in measurement time.

Conclusions

• Where we can evaluate them, the stratospheric channels on AMSU appear to be in better shape than the tropospheric channels.

• Need to come up with a reasonable diurnal adjustment– 4 AMSUs with different measurement times

– Stratospheric model data with output every 3 hours

– Microwave Limb Sounder probably not useful.