NOAA Technical Report NESDIS 124

Calibration of the Advanced Microwave Sounding 

Unit-A for NOAA-N’

Washington, D.C. 

September 2007

U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

National Environmental Satellite, Data, and Information Service 
 

NOAA TECHNICAL REPORTS 

National Environmental Satellite, Data, and Information Service 

 The National Environmental Satellite, Data, and Information Service (NESDIS) manages the 

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 Publication in the NOAA Technical Report series does not preclude later publication in scientific 

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reports appear below: 

NESDIS 96 Hydrography of the Ross Sea Continental Shelf During the Roaverrs, NBP96-06, Cruise 

 December 1996 - January 1997. Michael L. Van Woert, David Pryor, Eric Quiroz, Richard 

 Slonaker, and William Stone, September 2000. 

NESDIS 97 Hydrography of the Ross Sea Continental Shelf During the Roaverrs, NBP97-09, Cruise 

 December 1997 - January 1998. Michael L. Van Woert, Lou Gordon, Jackie Grebmeier, 

 Randal Holmbeck, Thomas Henderson, and William F. Van Woert, September 2000. 

NESDIS 98 NOAA-L and NOAA-M AMSU-A Antenna Pattern Corrections. Tsan Mo, August 2000. 

NESDIS 99 The Use of Water Vapor for Detecting Environments that Lead to Convectively Produced 

 Heavy Precipitation and Flash Floods. Rod Scofield, Gilberto Vicente, and Mike Hodges, 

 September 2000. 

NESDIS 100 The Resolving Power of a Single Exact-Repeat Altimetric Satellite or a Coordinated 

 Constellation of Satellites: The Definitive Answer and Data Compression. Chang-Kou Tai, 

 April 2001.

NESDIS 101 Evolution of the Weather Satellite Program in the U.S. Department of Commerce - A Brief 

 Outline. P. Krishna Rao, July 2001. 

NESDIS 102 NOAA Operational Sounding Products From Advanced-TOVS Polar Orbiting 

 Environmental Satellites. Anthony L. Reale, August 2001.

NESDIS 103 GOES-11 Imager and Sounder Radiance and Product Validations for the GOES-11 Science 

 Test. Jaime M. Daniels and Timothy J. Schmit, August 2001. 

NESDIS 104 Summary of the NOAA/NESDIS Workshop on Development of a Coordinated Coral Reef 

 Research and Monitoring Program. Jill E. Meyer and H. Lee Dantzler, August 2001.
 

NOAA Technical Report NESDIS 124

Calibration of the Advanced Microwave Sounding 

Unit-A for NOAA-N’

Tsan Mo 

NOAA/NESDIS/STAR 

5200 Auth Road 

Camp Springs, MD 20746 

Washington, DC 

September 2007 

U.S. DEPARTMENT OF COMMERCE 

Carlos M. Gutierrez, Secretary 

National Oceanic and Atmospheric Administration 

Vice Admiral Conrad C. Lautenbacher, Jr., U.S. Navy (Ret.), Under Secretary 

National Environmental Satellite, Data, and Information Service 

Mary Kicza, Assistant Administrator 
ii
iii

TABLE OF CONTENTS 

ABSTRACT ......................................................................................................................................1 

1. INTRODUCTION........................................................................................................................2 

2. DESCRIPTION OF CALIBRATION DATA..............................................................................4 

3. CALIBRATION ALGORITHM..................................................................................................7 

4. RESULTS.....................................................................................................................................9 

4.1 Calibration Accuracy .....................................................................................................9 

4.2 Nonlinearity..................................................................................................................10 

4.3 Simulated Quadratic Corrections to On-Orbit Data.....................................................13 

4.4 Temperature Sensitivity ...............................................................................................13 

4.5 Radiometric Counts as Function of Scene Target Temperature...................................19 

4.6 Channel gains ...............................................................................................................19 

5. CONCLUSION AND DISCUSSION ........................................................................................24 

ACKNOWLEDGMENTS...............................................................................................................24 

REFERENCES................................................................................................................................25 

APPENDIX A – NOAA-N’ CPIDS................................................................................................26 

APPENDIX B- NOAA POLAR ORBITER LEVEL 1B DATA ....................................................34 
iv

TABLE CAPTIONS

Table 1. NOAA-N’ AMSU-A1 SN 107 and AMSU-A2 SN 109 channel characteristics...............5 

Table 2. Number of PRTs in each calibration target .......................................................................6 

Table 3. Uncertainty in brightness temperatures and measurement errors .....................................7 

Table 4. NOAA-N’ AMSU-A: Nonlinearity parameters u in dimension of (m2-sr-cm

-1)/mW ....14 

Table A-1. NOAA-N’ AMSU-A1 SN 107: Polynomial coefficients for converting PRT 

 counts into temperatures ..............................................................................................27 

Table A-2. NOAA-N’ AMSU-A2 SN 109: Polynomial coefficients for converting PRT 

 counts into temperatures ..............................................................................................28 

Table A-3. NOAA-N’ AMSU-A warm load corrections (K) at three instrument 

 temperatures. ................................................................................................................30 

Table A-4. NOAA-N’ AMSU-A cold bias )TC ............................................................................31 

Table A-5. NOAA-N’: Error Limits of Warm and cold radiometric counts between samples 

 of same scan line.. ........................................................................................................32 

Table A-6. Pre-launch determined weight factors wk assigned to NOAA-N’ AMSU-A PRTs 

 in blackbody targets......................................................................................................32 

Table A-7. NOAA-N’ AMSU-A2 SN 109: Analog data conversion coefficients ........................33 

Table A-8. NOAA-N’ AMSU-A1 SN 107: Analog data conversion coefficients ........................33 
v

FIGURE CAPTIONS

Figure 1. NOAA-N’ AMSU-A: Calibration accuracies at three instrument temperatures ...........11 

Figure 2. NOAA-N’ AMSU-A: Pre-launch measured nonlinearities at three instrument 

 temperatures ...................................................................................................................12

Figure 3. NOAA-N’ AMSU-A: Simulated nonlinearity for on-orbit data.....................................15 

Figure 4. NOAA-N’ AMSU-A: Calibration results with PLLO #2 at Channels 9-14...................16

Figure 5. NOAA-N’ AMSU-A: Comparison of the measured NE)T values with specification 17 

Figure 6. NOAA-N’ AMSU-A: Measured NE)T as function of scene target temperatures.........18 

Figure 7. NOAA-N’ AMSU-A: Radiometric counts versus scene target temperature at three 

 instrument temperatures .................................................................................................20 

Figure 8. NOAA-N’ AMSU-A: Intercept counts at three instrument temperatures ......................21 

Figure 9. NOAA-N’ AMSU-A: Channel gains at three instrument temperatures .........................22 

Figure 10. NOAA-N’ AMSU-A: Calibration results with PLLO #2 at Channels 9-14, including 

 gains, radiometric counts, and intercept counts at three instrument temperatures.......23 
vi
CALIBRATION OF THE ADVANCED MICROWAVE SOUNDING UNIT-A 

FOR NOAA-N’

Tsan Mo 

NOAA/NESDIS

Center for Satellite Applications and Research 

5200 Auth Road, Camp Springs, MD 20746 

ABSTRACT

After successful launches of the Advanced Microwave Sounding Unit-A (AMSU-A) onboard the 

NOAA-K, -L, -M, -N, and the European Organization for the Exploitation of Meteorological 

Satellites (EUMETSAT) METeorological OPerational (METOP) satellite in 1998, 2000, 2002, 

2005,and 2006, receptively, the sixth AMSU-A will be launched onboard the NOAA-N’ in February 

2009. This report concerns the analysis and evaluation of the thermal-vacuum chamber calibration 

data from the AMSU-A1 SN 107 and AMSU-A2 SN 109 flight models (FM) for NOAA-N’. The 

pre-launch calibration data were analyzed to evaluate the instrument performance, including 

calibration accuracy, nonlinearity, and temperature sensitivity. Great effort was taken to understand 

the instrument’s radiometric performance as a function of instrument temperature. The calibration 

data provide a base for derivation of the calibration parameters input data sets (CPIDS) which will 

be incorporated into the operational calibration algorithms for producing the NOAA AMSU-A 1B 

data sets.

The nonlinearity parameters, which will be used to account the nonlinear contributions from an 

imperfect square-law detector, were determined from this data analysis. The existence and 

magnitude of nonlinearity in each channel were established and simulated with a quadratic formula 

for modeling the nonlinear contribution that was developed in the analysis of the NOAA-KLMN 

AMSU-A pre-launch calibration data. The model was characterized by a single parameter u, values 

of which were obtained for each channel via least-squares fit to the data. Quadratic corrections 

which would be expected from the on-orbit data after the launch of AMSU-A into space were 

simulated. In these simulations, the cosmic background radiance corresponding to a cold space 

temperature 2.73K was adopted as one of the two reference points of calibration. The largest 

simulated nonlinear correction is about 2 K. Experience learned from examining the previous 

AMSU-A on-orbit data provides a better understanding of the AMSU-A performance in space and 

helps process these pre-launch calibration data. The calibration information presented in this report 

will be useful for post launch on-orbit verification of the AMSU-A instrument performance. 
2

1. INTRODUCTION

On 13 May 1998, the NOAA-K, which is designated NOAA-15 after the launch, was successfully 

launched into a circular, near-polar orbit with an altitude of 833-km above the Earth and an 

inclination angle of 98.7E

 to the Equator. NOAA-15 carries the first of a series of new microwave 

total-power radiometers, the Advanced Microwave Sounding Units (AMSU-A and AMSU-B), 

which provide 20 channels for atmospheric temperature and moisture soundings. NOAA-L/16, 

which was launched on September 28, 2000, carries the second AMSU-A. The NOAA-M/17 

AMSU-A was successfully launched on June 24, 2002. NOAA-17 is the first NOAA satellite that 

has been launched into an orbit to cross the Equator at 1000 and 2200 local time. NOAA-N/18 was 

launched on May 20, 2005 and carried the first Microwave Humidity Sounder (MHS) which 

replaces AMSU-B for humidity sounding. 

The METOP-A, the first of three satellites of the EUMETSAT Polar System (EPS), was launched on 

October 19, 2006, from Baikonur Cosmodrome in Kazakhstan, carries on board a set of NOAA 

provided instruments, including AMSU-A. The METOP series is part of the Initial Joint PolarOrbiting Operational Satellite System (IJPS) constellation, along with the NOAA-N and -N' 

satellites. Under the IJPS, NOAA and EUMETSAT have agreed to provide instruments for each 

other's satellites. 

The AMSU-A is divided into two physically separate modules, each of which operates and 

interfaces with the spacecraft independently. The AMSU-A1 module uses two independent antennaradiometer systems (A1-1 and A1-2) to provide 12 channels in the range 50.3 to 57.3 GHz oxygen 

band for retrieving the atmospheric temperatures from the Earth’s surface to about 50 kilometers (or 

1 mb), and another channel at 89 GHz. The AMSU-A2, which has 2 channels at 23.8 and 31.4 GHz, 

are used to identify precipitation and correct the effect of surface emissivity, atmospheric liquid 

water, and water vapor on temperature sounding. These window channels are also used to derive 

rain rate, sea ice concentration, and snow cover. 

Table 1 lists some of the NOAA-N’ AMSU-A main channel characteristics, including channel 

frequency, number of bands, 3-dB RF band width, radiometric temperature sensitivity (or NE)T), 

antenna beam efficiency, polarization, and field of view (FOV) of angular beam width for each 

channel. More detailed information on the AMSU-A radiometers is reported elsewhere [1]. Each of 

the AMSU-A antenna systems has a nominal FOV of 3.3o

 at the half-power points and covers a 
3

cross-track scan of "48E20' (to beam centers) from the nadir direction with 30 Earth FOVs per scan 

line. Beam positions 1 and 30 are the outermost scan positions of the Earth views, while beam 

positions 15 and 16 (at "1.67o

 from nadir) straddle the nadir. Views of cold space and a black-body 

target at the end of a scan provide onboard calibration once every 8 seconds. 

EUMETSAT provides the MHS for humidity sounding. It has two channels at 89 and 157 GHz, 

respectively, two channels around the 183 GHz water vapor line, and another channel at 190 GHz. 

Detailed description of the MHS radiometric performance has been given elsewhere [2]. 

All of the AMSU-A flight models were tested and calibrated in a thermal-vacuum (TV) chamber by 

the contractor. These pre-launch TV calibration data were evaluated and analyzed to derive the 

calibration parameters input data set (CPIDS) which is used in the NOAA operational calibration 

algorithm to produce the AMSU-A 1B data sets. Particularly, there is a small nonlinearity (of the 

order of 1 K), which cannot be evaluated by the two-point calibration but is determined from the 

pre-launch calibration data. 

In this study, the TV test data from the AMSU-A1 SN 107 and AMSU-A2 SN 109 are analyzed and 

evaluated. The same procedure developed for NOAA-K AMSU-A calibration [1] is closely 

followed. Experience gained from examining the NOAA-15, -16, -17, and -18 AMSU-A on-orbit 

data provides a better understanding of the AMSU-A performance in space and helps inmprove the 

analysis of the pre-launch calibration data. 

In the following sections, the results from the data analysis are presented. Instrument performances 

evaluated in this analysis include calibration accuracy, nonlinearity, and radiometric temperature 

sensitivity (or NE)T, the noise-equivalent temperature). Section 1 gives an introduction and section 

2 presents a brief description of the TV chamber test data. The calibration algorithm is described in 

section 3. The results are presented in section 4. Conclusion and discussion are given in section 5. 

Tables of CPIDS for NOAA-N’ AMSU-A are given in Appendices A. A brief description of the 

NOAA Level 1B data is given in Appendix B. 

2. DESCRIPTION OF CALIBRATION DATA
4

C

Aerojet (now Northrop Grumman), the AMSU-A contractor, took the calibration data in a TV test 

chamber using the full scan mode. In this mode, AMSU-A scans through 30 Earth field of views 

(FOVs), the cold target, and the internal warm blackbody target once every 8 seconds. It takes one 

sample at each Earth FOV and two samples at the cold and warm targets, respectively. Since the 

scene calibration target was fixed at FOV 6 (31E40' from nadir), only radiometric counts from FOV 

6 are used for calibration. Each antenna system looks at its own individual cold, warm, and scene 

targets. A series of Platinum Resistance Thermometers (PRTs) were used to monitor the 

temperatures of these calibration targets. The numbers of PRTs used to measure the physical 

temperatures of the scene, cold, and warm calibration targets in each antenna system are given in 

Table 2 which also lists the channels provided by each AMSU-A antenna system. Channels 9-14 

have both primary and secondary phase locked loop oscillators (i.e. PLLO #1 and PLLO #2, 

respectively) built-in. The PLLO #2 will be used for backup if PLLO #1 fails in operation. Invar 

high-Q cavity stabilized local oscillators [3] are used in other channels. 

The physical temperatures of scene and cold targets measured by individual PRTs were provided in 

Kelvin (K) on Aerojet’s data packages. However, the data from the PRTs monitoring the warm 

blackbody targets are given in counts, which are proportional to the blackbody temperatures. One 

should note that the scene and cold targets used in the TV chamber will not be carried into space. 

The PRT counts from the warm blackbody targets must be converted to PRT temperatures. The 

normal approach of deriving the PRT temperatures from counts is a two-step process: (1) the 

resistance of each PRT in ohms is computed by a count-to-resistance look-up table provided by the 

manufacturer. In this study, we used a polynomial representation of the count-to-resistance 

relationship provided by Aerojet; and (2) the individual PRT temperature in degrees Celsius is 

obtained from an analytic PRT equation [4], which is described in Appendix A. However, the two 

steps can be compressed to a single step with negligible errors. This single step process, which has 

been used in the NOAA-KLMN and METOP-A calibrations, computes the PRT temperatures 

directly from the PRT counts, using a cubic polynomial 

T f Wk kj k

j

j

= =

∑

0

3

 (1) 

where TWk and Ck represent the temperature and count of the PRT k. The polynomial coefficients, 

fkj, are derived for each PRT in this study. Equation (1) also applies to 47 other housekeeping 
Table 1. NOAA-N’ AMSU-A1 SN 107 and AMSU-A2 SN 109 Channel Characteristics. 

Channel Frequency 

(MHz) Channel NE

ΔT (K)

Number

Specification Measureda

No. of

Bands

Measured 3-dB 

RF Bandwidth

(MHz) Spec. Measured

Beamb

Efficiency

1 23800 23800.47 1 251.08 0.30 0.172 97%2 31400 31401.37 1 160.08 0.30 0.170 98%3 50300 50300.41 1 160.24 0.40 0.213 97%4 52800 52800.74 1 380.40 0.25 0.136 95%5 53596 ± 115 53596.41 ± 115

2 167.86 | 167.86 0.25 0.160 96%

6 54400 54400.05 1 379.94 0.25 0.136 97%7 54940 54939.30 1 380.30 0.25 0.1650 97%8 55500 55500.69 1 310.12 0.25 0.172 95%9 fo = 57290.344 fo = 57290.332 1 310.12 0.25 0.178 96%

10 fo ± 217 fo ± 217

2 75.98 | 75.98 0.40 0.225

11 fo ± 322.2 ± 48 fo ± 322.2 ± 48

4 34.90 /35.29 |35.29 /34.90 0.40 0.240

12 fo ± 322.2 ± 22 fo ± 322.2 ± 22

4 15.44 / 15.47 | 15.47 / 15.44 0.60 0.349

13 fo ± 322.2 ± 10 fo ± 322.2 ± 10

4 7.82 / 7.85 | 7.85 / 7.82 0.80 0.506

14 fo ± 322.2 ± 4.5 fo ± 322.2 ± 4.5

4 2.95 / 2.96 | 2.96 / 2.95 1.20 0.829

15 89000 89010.00 1 1990.94 0.50 0.122 98%

aAt a temperature of 20o C for channels 1, 2, and 15; at 22o C for other channels. bMeasured. cSpecification is 3.3o ± 10%. 

5
6

Table 2. Number of PRTs in each calibration target and channels provided by 

individual antenna systems. The last row gives the number of scans collected 

in the calibration for each system 

Number of PRTs in each target Remarks 

Items 

A2 A1-2 A1-1 

Warm Target 7 5 5 

Cold Target 11 7 7 

Scene Target 11 7 7 One bad PRT in A1-2 

Three bad PRTs in A1-1

Channels 1 & 2 3, 4, 5 & 8 6, 7, & 9-15

PLLO#2 - - Ch. 9-14 Backup PLLO 

N(Scan No.) 120 400 to 900 400 to 900 See Note 

Note: For A1-1 & A1-2: N=400, 400, 550, 725, 725, and 900 when the 

scene target temperature at Ts=84, 130, 180, 230, 280, and 330K, respectively. 

temperature sensors, such as the mixers, the IF amplifiers and the local oscillators. These fkj

coefficients for all PRTs and housekeeping sensors in NOAA-N’ AMSU-A1 SN 107 and AMSU-A2 

SN 109 are listed in Appendix A (Tables A-1 and A-2, respectively). 

The mean internal blackbody temperature, TW, is calculated from the individual PRT temperatures, 

T

W T

W

W T

Wk

k

m

k

m

k

k

= + =

=

∑

∑

1

1

Δ W (2) 

where m represents the number of PRTs for each antenna system (as listed in Table 2) and Wk is a 

weight assigned to each PRT k. The quantity )TW is a warm load correction factor, which is derived 

for each channel from the TV test data at three instrument temperatures (low, nominal, and high). 

The procedure for determining the )TW values has been described elsewhere [5]. For each AMSU-A 

antenna system, a special set of calibration data was taken to determine the )TW values, which are 

given in Appendix A (Table A-3). The Wk value, which equals 1 (0) if the PRT k is determined 

good (bad) before launch. Similarly, the mean temperatures of cold targets are defined in the same 
7

way as in Equation (2), except without the term )TW. 

The TV calibration data were taken at three instrument temperatures and the scene target was cycled 

through six temperatures 84, 130, 180, 230, 280, and 330K, respectively, at each instrument 

temperature. At each of the scene target temperatures, calibration data were acquired for enough 

number of scans to assure an effective temperature sensitivity less than 0.03K. The number of scans 

required depends upon the expected NE)T of channel 14 (which has the largest NE)T) and is 

therefore a function of the scene target temperature. Actual numbers of scans taken at individual 

temperatures are given in Table 2. The uncertainties in knowledge of brightness temperatures and 

measurement errors were obtained by Aerojet [6, 7]. These are given Table 3. 

Table 3. Uncertainty in brightness temperatures and measurement errors. 

AMSU-A2 :Ch. 1 and 2 AMSU-A1: Ch. 3 - 15 

Source of Error 

Bias (K) Random (k) Bias (K) Random (k) 

Warm Target -0.050 "0.122 -0.050 "0.122 

Cold Target 0.024 "0.105 0.024 "0.091 

Scene Target 0.002 "0.101 0.002 "0.090 

Antenna beam widths at all channels were also measured and the values for NOAA-N’ AMSU-A 

are listed in Table 1. Antenna beam efficiency was calculated at each channel frequency and is 

listed in Table 1. 

3. CALIBRATION ALGORITHM

In this study, calculations of radiometric measurements and variables related to the calibration 

process are all performed in radiance with dimension of mW/(m2-sr-cm

-1), but the final results are 

presented in temperatures. All instruments flown on NOAA satellites produce measurements in 

radiance. Conversion between brightness temperature and radiance was performed using the full 

Planck function, instead of the Rayleigh-Jeans approximation. This also eliminates any possible 

conversion inaccuracy that may occur, particularly in the region of the space cosmic back-ground 

temperature -2.73K, where the Rayleigh-Jeans approximation breaks down. 
8

For each scan, the blackbody radiometric counts CW are the averages of two samples of the internal 

blackbody. Similarly, the space radiometric counts CC are the average of two samples of the space 

target. To reduce noise in the calibrations, the CX (where X=W or C) for each scan line were 

convoluted over several neighboring scan lines according to the weighting function [1] 

C

WC t

W

X

i Xi

i n

n

i

i n

n = = −

= −

∑

∑

( )

 (3) 

where ti (when i...0) represents the time of the scan lines just before or after the current scan line and 

t0 is the time of the current scan line. One can write ti = t0 + i)t, where )t = 8 seconds for AMSUA. The 2n+1 values are equally distributed about the scan line to be calibrated. Following the 

NOAA-KLM operational preprocessor software, the value of n=3 is chosen for all AMSU-A antenna 

systems. A set of triangular weights of 1, 2, 3, 4, 3, 2, and 1 is chosen for the weight factor Wi that 

appears in Equation (3) for the seven scans with i = -3, -2, -1, 0, 1, 2, and 3, respectively. 

The calibration algorithm [1], which takes into account the nonlinear contributions due to an 

imperfect square-law detector, converts scene counts to radiance RS as follows, 

RR RR ( ) C C

C C S W WC Q S W

W C

=+ − −

−

⎛

⎝

⎜ ⎞

⎠

⎟ + (4) 

where RW and RC are the radiance computed from the PRT blackbody temperature TW and the PRT 

cold target temperature TC, respectively, using the Planck function. The CS is the radiometric count 

from the Earth scene target. The averaged blackbody and space counts,CW and CC , are defined by 

Equation (3). 

The quantity Q, which represents the nonlinear contribution, is given by [1] 

( ) ( )( )

( ) Q uR R

CCCC

C C

W C

S W S C

W C

= − − −

−

2

2 (5) 

where u is a free parameter, values of which are determined at three instrument temperatures (low, 

nominal, and high). After launch, the u values at the actual on-orbit instrument temperatures will be 

interpolated from these three values. For channels 9-14 (AMSU-A1-1), two sets of the u parameters 
9

are provided; one set is for the primary PLLO#1 and the other one for the redundant PLLO#2. 

The quantity RS in Equation (4) represents the radiometric scene radiance of individual channels. 

For users of NOAA Level 1B data, a simplified formula, which converts CS directly into RS, is 

presented in Appendix B. It should be noted that the ratios in Equations (4) and (5) will eliminate 

the effect of any linear variation in the radiometric counts on RS. The channel gain, G, is defined as 

G

C C

R R

W

W C

= −

−

C

 (6) 

The quantity G varies with instrument temperature, which is defined as the RF Shelf temperature for 

each AMSU-A antenna system. For a fixed instrument temperature, G is approximately constant. 

The first two terms in Equation (4) constitute a linear two-point calibration equation, if the quadratic 

term is negligible. Let RSL denote these two terms, 

R R RR ( ) C C

C C SL W W C

S W

W C

=+ − −

−

⎛

⎝

⎜ ⎞

⎠

⎟ (7) 

The linear scene radiances RSL are calculated using the TV chamber test data. The results are 

discussed in the following section. 

4. RESULTS

4.1 Calibration Accuracy

The calibration accuracy, ΔR, is defined as the difference between the scene PRT radiance Rsprt and 

the radiometric scene radiance. It is calculated from the equation 

Δ R ( NR R sprt SL i i

N

= − ⎡

⎣

⎢ ⎤

⎦

⎥ =

∑ 1

1

) (8) 

where N is the number of scans at a specific scene temperatures (N= 120 for AMSU-A2 channels 

but ranging from 400 to 900 for AMSU-A1 channels). 

Equation (7) would be a good representation of the microwave radiometric scene radiance for a 

perfect square-law detector. Any deviation of the quantity RSL from the measured scene PRT 

radiance Rsprt indicates the presence of either nonlinearity in the radiometer system or some other 

potential source of contamination in the calibration data. 
10

Figure 1 shows the calculated calibration accuracies in temperature, )T (corresponding to )R), 

versus the scene PRT temperature for channels 1 through 15. The AMSU-A specification requires 

)T = 2.0 K for channels 1, 2, and 15, and )T = 1.5 K for all other channels. The results in Figure 1 

show that the )T values for the A1-1 channels do not meet the specification. 

4.2 Nonlinearity

The )T patterns (Figure 1) show clearly the nonlinearity patterns which can be represented by the 

quadratic formula Q defined in Equation (5). The nonlinearity of a channel is normally defined as 

the residuals from a least-squares fit of its scene PRT radiance as a linear function of the radiometric 

radiance RSL (Equation 7). The nonlinearity is defined as the differences (or residuals) between the 

Rsprt and the best-fit results from a linear equation in the form LinFit = a + b RSL (where a and b are 

the intercept and slope). These residuals, which are defined as the measured nonlinearity Q (= Rsprt 

- LinFit), are shown in Figure 2. The largest (absolute) Q value on each curve is defined as the 

measured nonlinearity that can be compared to those as defined in the AMSU-A specification. 

The results in Figure 2 show that the maximum (absolute) Q values are about 0.6K. The AMSU-A 

specification requires Q = 0.5K for channels 1, 2, and 15; and Q = 0.375K for other channels. All 

results at AMSU-A1-1 channels in Figure 2 do not meet the specifications. All of the curves, except 

channel 2, in Figure 2 have two roots, representing solutions of a quadratic equation, which can be 

written in the form 

Q uR R R R ( )( ) S S =− − 1 2 (9) 

where R1 and R2 represent the two roots. One can obtain a similar equation from Equation (5) by 

replacing the counts by its individual radiance, since the radiometric counts are proportional to 

radiance in a first-order approximation. The resultant equation represents a different straight line 

intersecting the same curve at RW and RC. Once the parameter u is determined, it can be used with 

any pair of roots to calculate Q. We applied Equation (9) to fit the quadratic curves in Figure 2 to 

obtain the u values with the two roots extracted from each plot. Table 4 gives the best-fit u values at 

three instrument temperatures for individual channels. 
11

Figure 1. NOAA-N’ AMSU-A: Calibration accuracies at three instrument temperatures. 
12

Figure 2. NOAA-N’ AMSU-A: Pre-launch measured nonlinearities at three instrument 

temperatures. 
13

4.3 Simulated Quadratic Corrections to On-Orbit Data 

Once the u values are determined, Equation (9) can be used to simulate the quadratic contributions 

which are expected from on-orbit data. This can be accomplished by replacing the roots R1 and R2

with the radiance R2.73 (corresponding to cold space temperature 2.73K) and RW, respectively. The 

simulated results are shown in Figure 3 for all channels at three instrument temperatures which are 

listed at the top of the plots. One should note that the instrument temperatures are different for the 

three AMSU-A antenna systems. The simulated quadratic contributions displayed in Figure 3 are 

larger than those shown in Figure 2. This is expected because the separation of the two reference 

calibration points is increased in the cases of simulations. Noticeable quadratic contributions appear 

in all channels, particularly the AMSU-A1-1 channels. The largest ones are approximately 2 K at 

several channels. It is important to note that the effect of instrument temperature on the quadratic 

contributions is nonlinear in general. 

Similarly, Figure 4 shows the calculated results which are associated with the redundant 

PLLO#2 built into channels 9-14. The left column of Figure 4 displays the calibration 

accuracies, )T, which are similar to Figure 1 and the middle column (corresponding to Figure 2) 

shows the residuals of the least-squares fit. The right column shows the simulated quadratic 

corrections, Q, which would occur in on-orbit data. 

4.4 Temperature Sensitivity

The specifications of temperature sensitivity (or NE)T) for AMSU-A channels are listed in 

Table 1. It is defined as the minimum change of a scene brightness temperature that can be 

detected. In practice, it is calculated as the standard deviation of the radiometer output (in K), 

when an antenna system is viewing a scene target at 300K. The calculated NE)T values are 

shown in Figure 5 together with the AMSU-A specifications. These calculated NE)T values 

correspond to a scene temperature of 300K. All of the calculated NE)T values in Figure 5 are 

better than those given in the AMSU-A specification. Actually, all NE)T values measured at all 

temperatures are better than the specification. The calculated NE)T values at all scene target 

temperatures and three instrument temperatures are shown in Figure 6. In general, the NE)T 

value decreases as the instrument temperature becomes colder. 
14

Table 4. NOAA-N’ AMSU-A: Nonlinearity parameters u in dimension of (m2-sr-cm-1)/mW. 

AMSU-A2 SN 109 channels: AMSU-A1-2 SN 107 channels:

Instrument 

Temp.(C) Ch. 2 Ch. 2 Instrument Temp.(C) Ch. 3 Ch. 4 Ch. 5 Ch. 

-7.26 5.045037 -0.802970 -2.49 0.945506 0.807438 0.595301 0.7620

11.53 5.329711 -0.264490 17.62 1.066226 1.072694 0.694163 0.969830.04 5.953661 0.114607 37.92 0.913515 0.974329 0.685200 0.9135

AMSU-A1-1 SN 107 channels: PLLO #1

Instrumen

t 

Temp.(C) 

Ch. 6 Ch. 7 Ch. 9 Ch. 10 Ch. 11 Ch. 12 Ch. 13 

-2.52 2.394737 2.50256

3

2.33563

3

1.82341

3 

2.060784 

2.401584 2.43565

4

17.47 2.320407 2.19148

6

2.02943

6

1.70867

3 

1.911764 

2.127352 2.15587

9

37.88 3.247517 3.06423

8

2.91783

3

2.59963

6 

2.688775 

2.971152 2.85521

6

AMSU-A1-1 SN 107 channels: PLLO #2

Instrument Temp. (C) Ch. 9 10 11 12 13 14 

-2.67 2.559711 2.028035 2.361547 2.702107 2.663920 3.309312

17.47 1.984376 1.692755 1.870282 2.096040 2.053746 2.48053937.60 2.541280 2.263376 2.355038 2.587566 2.527208 2.913724
15

Figure 3. NOAA-N’ AMSU-A: Simulated nonlinearities for on-orbit data. 
16

Figure 4. NOAA-N’ AMSU-A: Calibration results with PLLO #2 at Channels 9-14, (a) calibration 

accuracy, (b) measured nonlinearity, and (c) simulated on-orbit nonlinearity. 
17

Figure 5. NOAA-N’ AMSU-A: Comparison of the measured NEΔT values 

with specifications. 
18

Figure 6. NOAA-N’ AMSU-A: Measured NEΔT as a function of scene target temperatures at three 

instrument temperatures. 
19

4.5 Radiometric Counts as a Function of Scene Target Temperature

Figure 7 shows the plots of TV scene radiometric counts versus the scene PRT temperatures for all 

channels. The radiometric counts increase linearly with scene PRT temperatures ranging from 84 to 

330 K and good linear relationships exist between the radiometric counts and the scene PRT 

temperatures in the range 84 to 330 K. One can extrapolate these linear relationships to 0 K 

(corresponding to zero radiance) and obtain the intercepts for these plots. The intercept for each 

data point can also be computed from Equation (7) by setting RSL= 0 and solve for CS, which is 

denoted by CSint as 

C C GR S int W W = − (10) 

where G is the channel gain defined in Equation (6). The calculated CSint values at three instrument 

temperatures for each channel are shown in Figure 8. These are the mean values of all calculations 

performed with all available calibration data (from 120 to 900 scans as the scene temperature varies 

from 84 to 330 K). At each instrument temperature, the variation in the calculated CSint values is 

relatively small and all CSint values are positive. Figure 8 shows that the instrument temperature has 

a big impact on the magnitude of CSint, which increases as the instrument temperature decreases, 

except at channels 1, 2, and 8. 

4.6 Channel gains 

Values of the channel gains as defined in Equation (6) are also calculated from the TV calibration 

data. The gain values are converted into dimension of count/K. Figure 9 shows the calculated 

channel gains at three instrument temperatures, which are listed at the top of Figure 9. One should 

note that the abnormal behavior of channel 4 gain as a function of instrument temperature. 

Similarly, Figure 10 shows the calculated results of channel gain, radiometric counts, and intercept 

counts as a function of the scene PRT temperature when PLLO#2 was used. 
20

Figure 7. NOAA-N’ AMSU-A: Radiometric counts versus Scene target temperature at three 

instrument temperatures. 
21

Figure 8. NOAA-N’ AMSU-A: Intercept counts versus Scene target temperatures at three 

instrument temperatures. 
22

Figure 9. NOAA-N’ AMSU-A: Channel gain versus scene target temperatures at three 

instrument temperatures. 
23

Figure 10. NOAA-N’ AMSU-A: Calibration results as a function of scene target temperatures 

with PLLO #2 at three instrument temperatures. (a) gains, (b) radiometric counts, and 

(c) intercept counts 
24

5. CONCLUSION AND DISCUSSION

The TV chamber calibration data for the NOAA-N’ AMSU-A1 SN 107 and AMSU-A2 SN 109 

were analyzed to derive the CPIDS which will be used in the NOAA operational calibration 

algorithms to produce the AMSU-A 1B data sets. The results show that the instruments meet the 

AMSU-A specification in calibration accuracy and temperature sensitivity, but the measured 

nonlinearities at the AMSU-A1-1 channels do not meet the AMSU-A specification. 

The nonlinearity exists at all channels. A quadratic formula with a single parameter u is used to 

simulate these nonlinear contributions. The u values at three instrument temperatures were obtained 

from the pre-launch calibration data. Using the best-fit u values, the quadratic corrections which 

would be expected from the on-orbit data were simulated. In the simulations, the cold space 

radiance corresponding to 2.73K was adopted as one of the two reference calibration points (the 

other one is the internal blackbody temperature). The largest simulated nonlinear correction is about 

2 K as shown in Figure 3. 

Experience gained from examining the previous AMSU-A on-orbit data provides a better 

understanding of the AMSU-A performance in space and helps process the pre-launch calibration 

data. In general, the qualities of the calibration data are quite good. Particularly, the instrument 

temperatures were stabilized at pre-selected values with total variation less than "0.5K during each 

test cycle. This renders the measured instrument nonlinearities more reliable. The results presented 

in this study confirm the good quality of the AMSU-A instruments for NOAA-N’. The calibration 

information presented in this report will be immensely useful for post launch on-orbit verification of 

the AMSU-A instrument performance. 

Currently, AMSU-A SN 107 is under investigation of possible damage in an accident at Lockheed 

Martin. The analysis of the pre-launch calibration data will be redone if new calibration is required 

after any repair of damage. 

Acknowledgment 

The contents of this manuscript are solely the opinions of the author and do not constitute a 

statement of policy, decision, or position on behalf of NOAA or the U. S. Government. Aerojet, 

(now Northrop Grumman) was the primary AMSU-A contractor for building the instruments. 
25

REFERENCES

[1]. Tsan Mo, “Prelaunch Calibration of the Advanced Microwave Sounding Unit-A for 

NOAA-K,” IEEE Trans. Microwave Theory and Techniques, vol. 44, pp. 1460-1469, 1996. 

[2]. Tsan Mo and Kenneth Jarva, “Microwave Humidity Sounder Calibration Algorithm,” 

NOAA Technical Report NESDIS 116, October 2004. 

[3]. P. K. Patel and J. Mentall, “The Advanced Microwave Sounding Unit-A,” in Microwave 

Instrumentation for Remote Sensing of the Earth, SPIE Vol. 135, Orlando, April 13-14, 

1993, pp.130-135. 

[4]. PRT Handbook, Bulletin 1024, 1986, Rosemount Inc., Burnsville, MN 55337. 

[5]. Tsan Mo, “Calibration of the Advanced Microwave Sounding Unit-A for NOAA-K,” NOAA 

Technical Report NESDIS 85, June 1995. 

[6]. Calibration Log Book for AMSU-A2 SN 109,” Report No. 11331A, August 2006, Northrop 

Grumman, Azusa, CA 91702. 

[7]. Calibration Log Book for AMSU-A1 SN 107,” Report No. 11324C, August 2006, Northrop 

Grumman, Azusa, CA 91702. 

[8]. Tsan Mo, “AMSU-A Antenna Pattern Corrections,” IEEE Trans. Geoscience and Remote 

Sensing, vol. 37, pp. 103-112, 1999. 
26

Ck

APPENDIX A 

NOAA-N’ CPIDS : COEFFICIENTS OF AMSU-A1 SN 107 AND AMSU-A2 SN 109

A.1 Polynomial Coefficients for Converting PRT Counts into Temperatures

The two-step process for deriving the PRT temperatures from PRT counts Ck is briefly described 

here. First the count Ck from PRT k is converted into resistance rk (in ohms) by a polynomial 

r A k i

i

i

= =

∑

0

3

 (A-1) 

where the coefficients Ai for individual PRTs and temperature sensors were provided by Aerojet. 

Once the resistance rk is known, then one can calculate the PRT temperature t (in Celsius) from the 

Callendar-Van Dusen equation [4], which is given by 

r

r

t

ttt t t

o

=+ − −

⎛

⎝

⎜ ⎞

⎠

⎟ − − ⎛

⎝

⎜ ⎞

⎠

⎟ ⎛

⎝

⎜ ⎞

⎠

⎟ ⎡

⎣

⎢ ⎤

⎦

1 ⎥ 1001

100 100

1

100

3

αδ β (A-2) 

where: 

r resistance (in ohms) at temperature t (N t C) of the blackbody target 

r resistance at t = 0N o C (supplied by the manufacturer via Aerojet) 

$ 0 for t > 0NC, and 0.11 for t < 0N 

" and * are constants provided by the manufacturer via Aerojet. 

Calculation shows that the error is negligible by setting $ = 0 in Equation (A-2). In this study, it is 

assumed $ = 0 in all cases, then Equation (A-2) is simplified into a quadratic equation in t. In such 

case, one can solve the quadratic equation for t in terms of rt. Then the PRT temperature in degree 

Kelvin is obtained from t + 273.15. By this way, data sets of PRT temperatures versus counts for 

individual PRTs are computed. Then Equation (1) is applied to fit these data sets for obtaining the 

polynomial coefficients fkj for individual PRTs and housekeeping sensors. These best-fit coefficients 

are listed in Tables A-1 and A-2, respectively, for AMSU-A1 SN 107 and AMSU-A2 SN 109. Test 

calculations show that these polynomials are very accurate in reproducing temperatures of all 

sensors with errors in order of 0.01 K. 
27

Table A-1. NOAA-N’ AMSU-A1 SN 107: Coefficients for converting PRT counts into temperatures.

PRT fk0 fk1 fk2 fk3 Description 

1 263.1118 1.742062E-03 3.497049E-09 1.447318E-14 Al-1 MOTOR

2 263.7931 1.733920E-03 3.858388E-09 4.108136E-15 A1-2 MOTOR

3 264.0873 1.772267E-03 1.969058E-09 3.782504E-14 Al-1 FEED HORN 

4 263.7359 1.746087E-03 3.388829E-09 1.539593E-14 A1-2 FEED HORN 

5 263.4033 1.731448E-03 4.052407E-09 6.281552E-15 Al-1 RFMUX 

6 263.6212 1.736000E-03 3.594951E-09 1.264543E-14 Al-2 RFMUX 

7 262.6824 1.728847E-03 4.019764E-09 5.986536E-15 Ch. 3 DRO 

8 263.4037 1.735807E-03 3.885898E-09 8.667607E-15 CH. 4 DRO 

9 262.7392 1.731672E-03 3.496970E-09 1.431707E-14 CH. 5 DRO 

10 263.3888 1.740029E-03 3.520360E-09 1.251986E-14 CH. 6 DRO 

11 263.6862 1.735802E-03 3.586685E-09 1.647744E-14 CH. 7 DRO 

12 263.6868 1.744705E-03 3.305509E-09 1.818267E-14 CH. 8 DRO 

13 263.6375 1.732038E-03 3.697993E-09 1.205412E-14 CH. 15 GDO 

14 263.9067 1.734456E-03 3.429725E-09 1.544829E-14 CH.9 thru 14 PLO#2 

15 263.3486 1.753624E-03 3.516755E-09 3.333381E-15 CH.9 thru 14 PLO#1 

16 263.3486 1.753624E-03 3.516755E-09 3.333381E-15 NOT used (dummy) 

17 263.2393 1.744402E-03 3.362316E-09 1.334880E-14 CH. 3 MIXERAF 

18 263.6364 1.771411E-03 3.576661E-09 8.852903E-15 CH. 4 MIXER/IF 

19 263.8027 1.735185E-03 3.816865E-09 4.611234E-15 CH. 5 MIXER/IF 

20 263.9944 1.732857E-03 3.865460E-09 1.188194E-14 CH. 6 MIXER/IF 

21 263.5726 1.734105E-03 4.104094E-09 4.784842E-15 CH. 7 MIXER/IF 

22 263.1446 1.735692E-03 3.487495E-09 1.448047E-14 CH. 8 MIXERAF 

23 263.3230 1.736698E-03 3.506417E-09 1.381465E-14 CH.9 thru 14 MIXERAF 

24 263.8131 1.733783E-03 3.705516E-09 1.114634E-14 CH. 15 MIXER/IF 

25 263.5378 1.746153E-03 3.526695E-09 1.533726E-14 CH.11 thru 14 IF AM 

26 263.5392 1.735697E-03 3.888978E-09 1.279559E-14 CH. 9 IF AMP 

27 263.1599 1.731394E-03 3.924602E-09 7.025278E-15 CH. 10 IF AMP 

28 263.2114 1.735249E-03 3.437025E-09 1.482940E-14 CH. 11 IF AMP 

29 263.5982 1.739884E-03 3.453134E-09 1.511657E-14 DC/DC CONVERTER 

30 263.6745 1.740961E-03 3.504604E-09 1.020772E-14 CH. 13 IF AMP 

31 263.5161 1.740639E-03 3.555526E-09 1.322503E-14 CH. 14 IF AMP 

32 263.0495 1.754169E-03 3.485714E-09 9.320949E-15 CH. 12 IF AMP 

33 263.7456 1.728914E-03 3.995046E-09 6.167204E-15 Al-1 RFSHELF 

34 264.5479 1.742660E-03 3.626275E-09 1.254250E-14 A1-2 RFSHELF 

35 263.4284 1.726987E-03 3.945960E-09 7.127579E-15 DETECTOR/PRE-AMP 

36 254.8741 1.637893E-03 5.902597E-09 2.947544E-14 Al-1 WARM LOAD 1 

37 254.4845 1.634828E-03 5.860831E-09 2.909161E-14 Al-1 WARM LOAD 2 

38 254.5352 1.627381E-03 5.878626E-09 3.107089E-14 Al-1 WARM LOAD 3 

39 254.1389 1.638958E-03 5.777645E-09 2.745335E-14 Al-1 WARM LOAD4 

40 254.6330 1.636434E-03 5.860082E-09 2.914760E-14 A1-1 WARM LD CENTER

41 254.6251 1.637361E-03 5.846084E-09 3.029967E-14 A1-2 WARM LOAD 1 

42 254.6393 1.637848E-03 5.829585E-09 2.888881E-14 A1-2 WARM LOAD 2 

43 254.1602 1.630533E-03 5.839149E-09 3.010925E-14 A1-2 WARM LOAD 3 

44 255.0383 1.634408E-03 5.912973E-09 2.908720E-14 A1-2 WARM LOAD 4 

45 254.3306 1.632722E-03 5.889366E-09 2.895453E-14 A1-2 WARM LD CENTER
28

Table A-2. NOAA-N’ AMSU-A2 SN 109: Polynomial coefficients for converting PRT counts into 

 temperatures. 

PRT fk0 fk1 fk2 fk3 Description 

1 263.3287 1.742668E-03 4.311887E-09 2.025034E-16 Scan Motor 

2 263.3765 1.752967E-03 3.748854E-09 1.258927E-14 Feedhorn 

3 263.5512 1.739217E-03 3.818752E-09 1.353860E-14 RF Diplexer 

4 263.6189 1.749884E-03 3.816858E-09 1.067548E-14 Mixer/IF CH1 

5 263.9921 1.751035E-03 3.631815E-09 1.485421E-14 Mixer/IF CH2 

6 263.7419 1.753762E-03 3.693388E-09 1.127053E-14 CH 1 DRO 

7 263.4610 1.747977E-03 4.016104E-09 7.197988E-15 CH 2 DRO 

8 263.4379 1.763693E-03 3.358171E-09 1.355759E-14 Compensat Motor 

9 263.9190 1.751008E-03 4.282710E-09 2.331043E-15 Sub Reflector 

10 262.9899 1.747058E-03 3.705516E-09 1.233494E-14 DC/DC Converter 

11 263.5386 1.745205E-03 4.009926E-09 9.340984E-15 RF Shelf 

12 263.2827 1.749743E-03 4.089112E-09 6.352310E-15 Det. Pre-Amp 

13 254.4454 1.646443E-03 5.907230E-09 3.059857E-14 Warm Load Ctr 

14 254.3621 1.658168E-03 5.933477E-09 2.513103E-14 Warm Load #1 

15 254.8100 1.652669E-03 5.849476E-09 3.025275E-14 Warm Load #2 

16 254.1330 1.648472E-03 5.857347E-09 3.302980E-14 Warm Load #3 

17 254.9246 1.648978E-03 5.884300E-09 3.126444E-14 Warm Load #4 

18 254.7082 1.641230E-03 5.955578E-09 3.155298E-14 Warm Load #5 

19 254.6145 1.648466E-03 5.895623E-09 3.138678E-14 Warm Load #6 
29

A.2 Warm Load Correction

The in-flight warm load correction (WLC) was calculated according to a formula developed by 

Aerojet [6-7]. For each AMSU-A antenna system, a special set of calibration data were acquired by 

setting the temperature of its variable scene target equal to that of the internal blackbody (warm) 

target. The physical temperature TW of the internal blackbody target was determined from the PRT 

counts as described in Section 2. The radiometric temperature Twrad of the blackbody (in-flight 

warm load) was calculated (for each scan in the data set) by the formula 

T T TT ( ) C C

C C wrad sprt sprt C

W S

S C

=+ − −

−

⎛

⎝

⎜ ⎞

⎠

⎟ (A-3) 

where: 

Tsprt PRT temperature of the variable scene target, 

TC PRT temperature of the cold target, 

CW the average of two radiometric counts from the warm target, 

CC the average of two radiometric counts from the cold target, and 

CS radiometric counts from the variable scene target. 

One should note that temperatures, Tsprt and TC, from the scene and cold targets are used as the two 

reference calibration points in Equation (A-3) to calculate the radiometric temperature of the warm 

target. The in-flight warm load correction factor )TW was computed from the formula, 

Δ T ( N W w T T rad i

i

N

= − ⎡

⎣

⎢ ⎤

⎦

⎥ =

∑ 1

1

W ) (A-4) 

where N represents the number of scans in a data set. The )TW values at three instrument (RF Shelf) 

temperatures for each AMSU-A antenna system are listed in Table A-3. For AMSU-A1, the )TW

values for both PLLO#1 and PPLO#2 were calculated and listed. These )TW values will be used in 

both NOAA-N’ AMSU-A operational calibration algorithms. 
30

A.3 Nonlinearity parameters

The nonlinearity is discussed in Section 4.2 and the values of the nonlinearity parameter u are listed 

in Table 4. 

Table A-3. NOAA-N’ AMSU-A warm load corrections (K) at three instrument 

temperatures. 

 AMSU-A2 SN 109 Channels AMSU-A1-2 SN 107 Channels 

Instrument 

Temp.(C) Ch. 1 Ch. 2 InstrumentTemp.(C) Ch. 3 Ch. 4 Ch. 5 Ch.8 

-7.26 0.142 0.002 -2.49 -0.026 -0.002 -0.027 -0.087

11.53 0.062 0.008 17.62 0.093 0.009 0.005 -0.031

30.04 0.040 -0.029 37.92 0.041 -0.066 -0.066 -0.187

AMSU-A1-1 SN 107 Channels: PLLO#1:

Instrument 

Temp.(C) Ch. 6 Ch. 7 Ch. 9 Ch. 10 Ch. 11 Ch. 12 Ch. 13 Ch. 14 Ch. 15

-2.52 0.338 0.339 0.324 0.375 0.349 0.321 0.309 0.379 0.348 

17.47 0.442 0.416 0.403 0.405 0.419 0.411 0.426 0.403 0.396 

37.88 0.499 0.538 0.506 0.481 0.487 0.498 0.511 0.459 0.470 

AMSU-A1-1 SN 107 Channels: PLLO#2: 

Instrument 

Temp.(C) Ch. 9 Ch. 10 Ch. 11 Ch. 12 Ch. 13 Ch. 14 

-2.67 0.281 0.282 0.288 0.272 0.243 0.209 

17.47 0.722 0.717 0.731 0.692 0.703 0.721 

37.60 0.278 0.313 0.283 0.281 0.280 0.281 
31

T

A.4 Correction to In-orbit Cold Space Calibration

For on-orbit cold space calibration, there is an uncertainty due to antenna side lobe interference with 

the Earth limb and spacecraft. The contribution from this uncertainty should be added to the cold 

space cosmic background temperature of 2.73K. Therefore, the “effective ” cold space temperature 

TEC can be represented by 

T (A-5) EC C = 2 73 . + Δ

where )TC represents the contribution from the antenna side-lobe interference with the Earth limb 

and spacecraft. Estimates of )TC for individual channels of NOAA-N’ AMSU-A are made from the 

measured antenna pattern data [8]. These estimated )TC values for the four available cold 

calibration positions are listed in Table A-4. 

Table A-4. NOAA-N’ AMSU-A cold bias )TC. 

Pos. ID Angle Ch. 1 Ch. 2 Ch.4 Ch. 8 Ch. 15 a Ch. 3 Ch. 5 Ch. 6 Ch. 7 Ch. 9 

1 83.333 1.34 0.48 1.83 2.19 1.47 1.32 1.69 1.73 1.57 0.61

2 81.667 1.33 0.45 1.67 2.03 1.38 1.20 1.57 1.59 1.45 0.57

3 80.000 1.33 0.44 1.60 1.94 1.34 1.14 1.5 1.52 1.38 0.55

4 76.667 1.33 0.44 1.50 1.84 1.28 1.08 1.42 1.45 1.31 0.53

 a Measured from nadir. 

A.5 Limit of Blackbody and Cold Counts Variation

For each scan, the blackbody counts CW is the average of two samples. If the two samples of the 

blackbody differ by more than a pre-set limit of blackbody count variation )CW, the data in the scan 

will not be used. The )CW values for individual channels are listed in Table A-5. These )CW

values, which equal approximately 3F (where F is the standard deviation of the internal blackbody 

counts), are calculated from the TV calibration data. Similarly, the cold count is the same. 
32

Table A-5. NOAA-N’: Error Limits of Warm and cold radiometric counts between 

 samples of same scan line. 

Limit Ch.1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 

Warm 18 18 18 18 18 18 18 18 18 18 24 24 30 60 22 

Cold 18 18 18 18 18 18 18 18 18 18 24 24 30 60 22 

A.6 Pre-launch Determined Weight Factors wk for the Internal Blackbody PRTs

The weight factors wk (see Equation 2) assigned to individual PRTs in the internal blackbody 

targets are listed in Table A-6. All NOAA-N’ AMSU-A PRTs are good. 

Table A-6. Pre-launch determined weight factors wk assigned to NOAA-N’ AMSU-A 

 PRTs in blackbody targets. 

Antenna 

w1 w2 w3 w4 w5 w6 w7 System 

AMSU-A2 1 1 1 1 1 1 1 

AMSU-A1-1 1 1 1 1 1 

AMSU-A1-2 1 1 1 1 1 

A.7 Conversion Coefficients of Analog Data

AMSU-A instrument has an analog telemetry bus to monitor key temperatures and voltages through 

the spacecraft. The resolutions of the analog telemetry received on the ground is 20 mV for one part 

in 256. To convert the analog data into physical quantities y, one must multiply the analog values by 

0. 02V (20 mV) to obtain the measured output, x, in volts and then uses the conversion equation, 

y = B + M x (A-6) 

where the values of B and M are given in Tables A-7 and A-8 for NOAA-N’ AMSU-A2 SN 109 

and AMSU-A1 SN 107, respectively. 
33

 Table A-7. NOAA-N’ AMSU-A2 SN 109: Analog data conversion coefficients. 

UIIS 

Ref.

Description y M B 

1 Scanner Motor Temperature K 68.027 0 

2 Comp Motor Temperature K 68.027 0 

3 R.F. Shelf Temperature K 68.027 0 

4 Warm Load Temperature K 68.027 0 

5 Comp. Motor Current (average) mA 46.6 0 

6 Ant Drive Motor Current (ave) mA 46.6 0 

7 Signal Processing +15Vdc v 4.315 0 

8 Antenna Drive +15Vdc v 4.315 0 

9 Signal Processing -1 5Vdc v 2.504 -22.562 

10 Antenna Drive - 15Vdc V 2.504 -22.562 

11 Mixer/IF Amplifier +10 Vdc V 2.889 0 

12 Signal Processing +5Vdc V 1.667 0 

13 Antenna Drive +5Vdc V 1.667 0 

14 Local Oscillator +lOVdc. (ch.1) V 2.861 0 

15 Local Oscillator +lOVdc (ch.2) V 2.861 0 

 Table A-8. NOAA-N’ AMSU-A1 SN 107: Analog data conversion coefficients. 

Pin # Description y M B 

3 Al-1 Scanner Motor Temperature K 68.027 0

22 A1-2 Scanner Motor Temperature K 68.027 0

2 A1-1 RF Shelf Temperature K 68.027 0

21 Al-2 RF Shelf Temperature K 68.027 0

4 Al-1 Warm Load Temperature K 68.027 0

23 Al-2 Warm Load Temperature K 68.027 0

8 Al-1 Antenna Drive Motor Current mA 23.3 0

27 Al-2 Antenna Drive Motor Current mA 23.3 0

11 Signal Processing (+15 VDC) v 4.315 0

9 Antenna Drive (+15 VDC) v 4.315 0

29 Signal Processing (-15 VDC) v 2.504 -22.562 

28 Antenna Drive (-15 VDC) v 2.504 -22.562 

34 Receiver Amplifiers (+8 VDC) v 2.50 0

12 Signal Processing (+5 VDC) v 1.667 0

10 Antenna Drive (+5 VDC) v 1.667 0

17 Receiver Mixer/IF (+10 VDC) v 2.889 0

16 Phase Lock Loop Ch 9/14 (+15 VDC) v 4.315 0

33 Phase Lock Loop Ch 9/14 (-15 VDC) v 2.504 -22.562 

13 Ch 3 L.O. Voltage (50.3 GHz) v 2.861 0

30 Ch 4 L.O. Voltage (52.8 GHz) v 2.861 0

14 Ch 5 L.O. Voltage (53.596 GHz) v 2.861 0

31 Ch 6 L.O. Voltage (54.4 GHz) v 2.861 0

15 Ch 7 L.O. Voltage (54.94 GHz) v 2.861 0

32 Ch 8 L.O. Voltage (55.5 GHz) v 2.861 0

25 PLLO Primary Lock Detect (PLO #1) v 1.0 0

6 PLLO Redundant Lock Detect (PLO #2) v 1.0 0

18 Ch 15 L.O. Voltage (89.0 GHz) v 4.315 0
34

S

APPENDIX B 

NOAA POLAR ORBITER LEVEL 1B DATA 

The NOAA Polar Orbiter Level 1B data are raw data that have been quality controlled and 

assembled into discrete data sets, to which Earth location and calibration information are appended 

but not applied. For simplification of application, the conversion of scene counts CS into scene 

radiance RS is accomplished by writing Equation (4) as 

R a aC aC S S =+ + 01 2

2 (B-1) 

where the calibration coefficients ai ( where i = 0, 1, and 2), which are output in the 1B data sets 

for individual scans, are expressed in terms of averaged calibration counts (over 7 scans) and 

calibration target temperatures. Derivation of these coefficients is described in the NOAA KLM 

User’s Guide. In Equation (B-1), there is a quadratic term which represents the nonlinearities in 

the measurements [1]. Users, who prefer scene temperature instead of radiance, can make the 

simple conversion, 

T BR( ) S = −1

S (B-2) 

where B-1(RS) is the inverse of the Planck function for radiance RS. The TS is the converted 

antenna scene temperature. 

The above calibration process applies to all AMSU-A measurements from NOAA-15, -16, -17, 

18, and –N’. 
NESDIS 105 Validation of SSM/I and AMSU Derived Tropical Rainfall Potential (TRaP) During the 

 2001 Atlantic Hurricane Season. Ralph Ferraro, Paul Pellegrino, Sheldon Kusselson, 

 Michael Turk, and Stan Kidder, August 2002. 

NESDIS 106 Calibration of the Advanced Microwave Sounding Unit-A Radiometers for NOAA-N and 

 NOAA-N=. Tsan Mo, September 2002. 

NESDIS 107 NOAA Operational Sounding Products for Advanced-TOVS: 2002. Anthony L. Reale, 

 Micheal W. Chalfant, Americo S. Allergrino, Franklin H. Tilley, Michael P. Ferguson, and 

 Michael E. Pettey, December 2002. 

NESDIS 108 Analytic Formulas for the Aliasing of Sea Level Sampled by a Single Exact-Repeat 

 Altimetric Satellite or a Coordinated Constellation of Satellites. Chang-Kou Tai, 

 November 2002. 

NESDIS 109 Description of the System to Nowcast Salinity, Temperature and Sea nettle (Chrysaora 

 quinquecirrha) Presence in Chesapeake Bay Using the Curvilinear Hydrodynamics in 

 3-Dimensions (CH3D) Model. Zhen Li, Thomas F. Gross, and Christopher W. Brown, 

 December 2002. 

NESDIS 110 An Algorithm for Correction of Navigation Errors in AMSU-A Data. Seiichiro Kigawa 

 and Michael P. Weinreb, December 2002. 

NESDIS 111 An Algorithm for Correction of Lunar Contamination in AMSU-A Data. Seiichiro 

Kigawa 

 and Tsan Mo, December 2002. 

NESDIS 112 Sampling Errors of the Global Mean Sea Level Derived from Topex/Poseidon Altimetry. 

 

 Chang-Kou Tai and Carl Wagner, December 2002. 

NESDIS 113 Proceedings of the International GODAR Review Meeting: Abstracts. Sponsors: 

 Intergovernmental Oceanographic Commission, U.S. National Oceanic and 

Atmospheric 

 Administration, and the European Community, May 2003. 

NESDIS 114 Satellite Rainfall Estimation Over South America: Evaluation of Two Major Events. 

 Daniel A. Vila, Roderick A. Scofield, Robert J. Kuligowski, and J. Clay Davenport, 

 May 2003. 

NESDIS 115 Imager and Sounder Radiance and Product Validations for the GOES-12 Science Test. 

 Donald W. Hillger, Timothy J. Schmit, and Jamie M. Daniels, September 2003. 

NESDIS 116 Microwave Humidity Sounder Calibration Algorithm. Tsan Mo and Kenneth Jarva, 

 October 2004. 

NESDIS 117 Building Ocean Profile-Plankton Databases for Climate and Ecosystem Research. 

 Sydney Levitus, Satoshi Sato, Catherine Maillard, Nick Mikhailov, Pat Caldwell, and 

 Harry Dooley (Retired), June 2005. 

NESDIS 118 Simultaneous Nadir Overpasses for NOAA-6 to NOAA-17 Satellites from 1980 to 2003 

for 

 the Intersatellite Calibration of Radiometers. Changyong Cao, Mitch Goldberg, 

 Fuzhong Weng, Cheng-Zhi Zou, and Pubu Ciren, August 2005. 

NESDIS 119 Calibration and Validation of NOAA-18 Instruments. Fuzhong Weng and Tsan Mo, 

 December 2005. 

NESDIS 120 THE NOAA/NESDIS/ORA WindSat Calibration/Validation Collocation Database. 

Larry Connor, February 2006. 

NESDIS 121 Calibration of the Advanced Microwave Sounding Unit-A Radiometer for METOP-A. 

Tsan Mo, August 2006. 

NESDIS 122 JCSDA Community Radiative Transfer Model (CRTM). Yong Han, Paul van Delst, 

Quanhua Liu, Fuzhong Weng, Banghua Yan, Russ Treadon, and John Derber, 

December 2005. 

NESDIS 123 Comparing Two Sets of Noisy Measurements. Lawrence E. Flynn, November 2006. 

NOAA SCIENTIFIC AND TECHNICAL PUBLICATIONS 

 The National Oceanic and Atmospheric Administration was established as part of the Department of 

Commerce on October 3, 1970. The mission responsibilities of NOAA are to assess the socioeconomic 

impact of natural and technological changes in the environment and to monitor and predict the state of the 

solid Earth, the oceans and their living resources, the atmosphere, and the space environment of the Earth. 

 The major components of NOAA regularly produce various types of scientific and technical information 

in the following types of publications: 

PROFESSIONAL PAPERS - Important definitive 

research results, major techniques, and special 

investigations. 

TECHNICAL SERVICE PUBLICATIONS - Reports 

containing data, observations, instructions, etc. 

 A partial listing includes data serials; prediction 

and outlook periodicals; technical manuals, 

training papers, planning reports, and 

information serials; and miscellaneous technical 

publications. 

CONTRACT AND GRANT REPORTS - Reports 

prepared by contractors or grantees under 

NOAA sponsorship. 

ATLAS - Presentation of analyzed data generally 

in the form of maps showing distribution of rainfall, chemical and physical conditions of oceans 

and atmosphere, distribution of fishes and 

marine mammals, ionospheric conditions, etc. 

TECHNICAL REPORTS - Journal quality with 

extensive details, mathematical developments, 

or data listings. 

TECHNICAL MEMORANDUMS - Reports of 

preliminary, partial, or negative research or 

technology results, interim instructions, and the 

like. 

 U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

National Environmental Satellite, Data, and Information Service 

Washington, D.C. 20233