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History of modifications
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AMSU-B | Advanced Microwave Sounding Unit-B | ||
MHS | Microwave Humidity Sounder Unit | ||
Satellites | AMSU-B: NOAA-15, NOAA-16, NOAA-17MHS: NOAA-18, NOAA-19, MetOp-A, MetOp-B | ||
Mission | Humidity sounding in almost all-weather conditions and precipitation rate | ||
Instrument type | Absorption-band MW radiometer/spectrometer - 5-channels | ||
Scanning technique | Cross-track: 90 steps of 16 km at sub satellite point, swath 2180 km (2250 km) for MHS (AMSU-B) Along-track: one 16-km line every 8/3 s | ||
Coverage/cycle | Near-global coverage twice/day | ||
Resources | Mass: 63 kg – Power: 93 W – Data rate: 3.9 kbps | ||
MHS/AMSU-B | MHS/AMSU-B channel bandwidth (MHz) | MHS/AMSU-B channel polarisation | MHS/AMSU-B channel radiometric accuracy (NEΔT) |
89.0 | 2800/1000 | QV/QV | 0.22/0.37 K |
157.0/150.0 | 2800/1000 | QV/QV | 0.38/0.84 K |
183.31 ± 3.0 | 2000/2000 | QH/QV | 0.42/0.60 K |
183.31 ± 1.0 | 1000/500 | QH/QV | 0.57/0.70 K |
190.311/183.31 ± 7 | 2000/1000 | QV/QV | 0.45/1.06 K |
Other datasets used to develop and test the NN algorithm are:
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Centre Frequency [GHz] | Polarization | Pixel Integration Time [ms] | Samples per scan | Inter-Scan Period [s] | Along-track Sample Spacing [km] | 3 dB Footprint Size |
19.35 | v/h | 7.95 | 64 | 3.8 | 25 | 69 × 43 |
22.235 | v | 7.95 | 64 | 3.8 | 25 | 50 × 40 |
37.0 | v | 7.95 | 64 | 3.8 | 25 | 37 × 28 |
37.0 | h | 7.95 | 64 | 3.8 | 25 | 37 × 29 |
85.5 | v/h | 3.89 | 128 | 1.9 | 12.5 | 15 × 13 |
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Altitude | 860 km |
Inclination | 98.8 ° |
Orbit Period | 102 min |
Swath Width | 1394 km |
Effective Scan Angle | 102.4 ° |
Local Zenith Angle | 53.1 ° |
Calibration Method | On board; each scan; fixed cold space reflector and reference black body hot load |
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1.2.2 The SSMIS Instrument
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Table 4: Summary of SSMIS channel characteristics exploited in the precipitation retrieval Anchor table4 table4
Channel | Centre Frequency [GHz] | Polarization | Pixel Integration Time [ms] | Samples per scan | Inter-Scan Period [s] | Along-track Sample Spacing [km] | 3 dB Footprint Size |
12 | 19.35 | h | 8.44 | 90 | 3.8 | 25 | 73.6 × 46.5 |
13 | 19.35 | v | 8.44 | 90 | 3.8 | 25 | 73.6 × 46.5 |
14 | 22.235 | v | 8.44 | 90 | 3.8 | 25 | 73.6 × 46.5 |
15 | 37.0 | v | 8.44 | 90 | 3.8 | 25 | 45.0 × 31.2 |
16 | 37.0 | h | 8.44 | 90 | 3.8 | 25 | 45.0 × 31.2 |
17 | 91.655 | v | 4.22 | 180 | 1.9 | 12.5 | 15.5 × 13.2 |
18 | 91.655 | h | 4.22 | 180 | 1.9 | 12.5 | 15.5 × 13.2 |
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Altitude | 833 km |
Inclination | 98.9 ° |
Orbit Period | 101.8 min |
Swath Width | 1707 km |
Effective Scan Angle | 143.2 ° |
Local Zenith Angle | 53.1 ° |
Calibration Method | On board; each scan; fixed cold space reflector and reference black body warm target |
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1.2.3 The AMSR-E Instrument
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Centre Frequency [GHz] | Bandwidth | Polarization | Pixel Integration Time [ms] | Scan cycle | Sampling Interval | IFOV |
6.925 | 350 | h/v | 2.6 | 1.5 | 10 × 10 | 74 × 43 |
10.65 | 100 | h/v | 2.6 | 1.5 | 10 × 10 | 51 × 30 |
18.7 | 200 | h/v | 2.6 | 1.5 | 10 × 10 | 27 × 16 |
23.8 | 400 | h/v | 2.6 | 1.5 | 10 × 10 | 31 × 18 |
36.5 | 1000 | h/v | 2.6 | 1.5 | 10 × 10 | 14 × 8 |
89.0 | 3000 | h/v | 1.3 | 1.5 | 5 × 5 | 6 × 4 |
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Altitude | 705 km |
Inclination | 98.2 ° |
Orbit Period | 98.8 min |
Swath Width | 1445 km |
Effective Scan Angle | 122 ° |
Earth Incidence Angle | 55 ° |
Calibration Method | On board; each scan; fixed cold space reflector and reference black body warm target |
The IFOVs of AMSR-E and SSM/I / SSMIS were harmonized by averaging the brightness temperatures of each three neighbouring AMSR-E scan positions.
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Channel | Centre Frequency [GHz] | Polarization | Pixel Integration Time [ms] | EFOVs per scan | EFOV | Inter-Scan Period [s] | IFOV |
1 | 10.65 | v | 6.6 | 104 | 63.2 × 9.1 | 6.6 | 59.0 × 35.7 |
2 | 10.65 | h | 6.6 | 104 | 63.2 × 9.1 | 6.6 | 60.1 × 36.4 |
3 | 19.35 | v | 6.6 | 104 | 30.4 × 9.1 | 6.6 | 30.5 × 18.4 |
4 | 19.35 | h | 6.6 | 104 | 30.4 × 9.1 | 6.6 | 30.1 × 18.2 |
5 | 21.3 | v | 6.6 | 104 | 22.6 × 9.1 | 6.6 | 27.2 × 16.5 |
6 | 37.0 | v | 6.6 | 104 | 16.0 × 9.1 | 6.6 | 16.0 × 9.7 |
7 | 37.0 | h | 6.6 | 104 | 16.0 × 9.1 | 6.6 | 16.0 × 9.7 |
8 | 85.5 | v | 3.3 | 108 | 7.2 × 4.6 | 3.3 | 6.7 × 4.1 |
9 | 85.5 | h | 3.3 | 108 | 7.2 × 4.6 | 3.3 | 6.9 × 4.2 |
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Altitude | 402 km |
Inclination | 35 ° |
Swath Width | 758.5 km |
Effective Scan Angle | 130 ° |
Earth Incidence Angle | 52.8 ° |
Calibration Method | On board; each scan; fixed cold space reflector and reference black body warm target |
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Variable | Data source |
Sea ice information (daily) | ECMWF ERA5 |
Snow cover information (daily) | ECMWF ERA5 |
2 m temperature (monthly) | ECMWF ERA5 |
Freezing level (monthly) | ECMWF ERA5 |
Sea ice cover (monthly) | ECMWF ERA5 |
Snow depth (monthly) | ECMWF ERA5 |
Total column integrated water vapor (monthly) | ECMWF ERA5 |
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Instrument | GPM DPR | |
KaPR | KuPR | |
Launch time | 27 Feb 2014 | 27 Feb 2014 |
Altitude (km) | 407 | 407 |
Inclination angle (°) | 65 | 65 |
Frequency (GHz) | 35.547 and 35.553 | 13.597 and 13.603 |
Horizon resolution at nadir (km) | 5 | 5 |
Swath width (km) | 120 | 245 |
Vertical resolution (m) | 250/500 | 250 |
Minimum detectable Ze (dBZ) | 12 (KaHS) | 18 |
Measurement accuracy (dBZ) | < ± 1 | < ± 1 |
Anchorsection3_2_2_2 section3_2_2_2
3.2.2.2 The NN training dataset
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Period | 1/01/2015 – 31/12/2016 |
Geographical area | 67 °S – 67 °N, 180 °W – 180 °E |
Number of MHS orbits | 36,856 |
Number of pixels with precipitation | 3,000,000 |
Horizontal resolution (Km) | 16 km × 16 km (nadir) 26 km × 52 km (scan edge) |
Reference precipitation product | 2B-CMB level-2 GMI/DPR combined V06A on Ku-band radar swath (NS) |
MHS BTs | FIDUCEO FCDR v4.1 |
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Variable in the database | Data source |
Latitude (MHS pixel) | FIDUCEO FCDR v4.1 |
Longitude (MHS pixel) | FIDUCEO FCDR v4.1 |
Mean Time (of DPR pixels within the ATMS pixel) | 2B-CMB level-2 GMI/DPR combined V06A |
Surface precipitation rate | 2B-CMB level-2 GMI/DPR combined V06A |
Precipitation liquid fraction information | 2B-CMB level-2 GMI/DPR combined V06A |
Time of MHS pixel | FIDUCEO FCDR v4.1 |
MHS Scan position | FIDUCEO FCDR v4.1 |
Sea ice information | ECMWF ERA5 |
2 m temperature | ECMWF ERA5 |
Total column integrated water vapor | ECMWF ERA5 |
Freezing level | ECMWF ERA5 |
Snow depth | ECMWF ERA5 |
Land/Sea Mask | ESA |
Anchorsection3_2_3 section3_2_3 _heading h.17dp8vu
3.2.3 Algorithm Flowchart
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Table 14: PNC module input variables. Anchor table14 table14
Input Variable | Variable dimensions | Variable type |
BT | 5 | Instantaneous |
monthly T2m | 1 | Average |
monthly FL | 1 | Average |
monthly TPWV | 1 | Average |
daily SD | 1 | Average |
daily SIF | 1 | Average |
ANG | 1 | Static |
OLC | 1 | Static |
The static and average variables determine a sort of a priori status of the atmosphere, allowing the NN to correctly interpret the radiative signal (after applying a zenith correction, if necessary): for example, a depression in the BT around the 157 GHz window channel is commonly due to the scattering of precipitating particles. However, if the atmosphere is sufficiently dry, the emission signature of a radiatively cold surface may lead to the same effect on the measured BT. Through the use of the ancillary data the NN aims to discriminate these different states.
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Variable Type | Input Variable | Variable dimension | Variable type |
BT | 89.0 GHz | 3 | Instantaneous |
BT Differences | 183.31 ± 3.0–183.31 ± 1.0 GHz | 5 | Instantaneous |
Model Derived Ancillary Variables | monthly T2m (K) | 5 | Average |
Ancillary Variables | ANG | 2 | Static Map |
The performance analysis of the PRE module was carried out using the 2016 dataset, which is an independent part of the observational MHS-DPR coincidence database, not used in the training and design phase of the algorithm (about 1.5 million points) (see section 3.2.2.2).
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| Ocean | Land |
BIAS[mm/h] | 0.02 | 0.01 |
CC | 0.75 | 0.70 |
RMSE[mm/h] | 1.02 | 1.08 |
Another result of the verification study is shown in figure 7. It shows the 2D histogram of the surface precipitation rate estimates from the NN and the corresponding values in the 2B-CMB dataset over ocean and land. Only pixels for which both the neural network and the 2B-CMB provided rainfall estimates ≥ 0.1 mm/h (TP pixels) were considered. In the scatterplot, the logarithmic axes represent the precipitation rate (NN vs. GPM 2B-CMB referred to as DPR), while the colour represents the number of points in the dataset for each 2D precipitation rate bin. Most of the points are close to the main diagonal for both ocean and land, with slight overestimation of very low precipitation (precipitation rate < 0.5 mm/h) over land by the NN.
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BQF | Occurred Condition |
0 | Precipitation Probability Index |
1 | Radiometer Scan index |
2 | Quality of input data |
3 | Background surface index (Snow) |
4 | Background surface index (Sea Ice) |
5 | Orography index |
6 | High Latitudes Index |
7 | Calibration Index |
8 | Invalid Data |
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Figure 11: Distribution of the QF index (percentage over all the available observations) for the year 2017.
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AMSU-B / MHS (PNPR-CLIM) | SSM/I / SSMIS (HOAPS v4) | AMSR-E2 (HOAPS v4 extended) | TMI (HOAPS v4 extended) | |||
Along-scan |
| 15.5 | 15.5 | 9 | ||
Cross-scan |
| 22.5 | 22.5 | 16 |
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Version | Description |
1.0 | Precipitation rates are derived from the original algorithm as described in this document. The version number is valid for daily and monthly files. |
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Variable Name | Dimension(s) | Unit | Description | |
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lat | 1 | °N (degrees North) | Latitude of grid cell centre | |
lat_bnds | 2 | °N (degrees North) | Boundaries of top (northern) and bottom (southern) grid cell edge | |
lon | 1 | °E (degrees East) | Longitude of grid cell centre | |
lon_bnds | 2 | °E (degrees East) | Boundaries of left (western) and right (eastern) grid cell edge | |
time | 1 | Seconds since 1970-01-01 | Time stamp of the current day | |
time_bnds | 2 | Seconds since 1970-01-01 | Boundaries of the time interval covered by time variable | |
platform_id | 1 | N/A | An integer used for internal platform assignment | |
instrument_id | 1 | N/A | An integer used for internal instrument assignment | |
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precip | 3 (time, lat, lon) | mm/d | Daily accumulated precipitation rates that are represented by a single multi-platform composite | |
precip_stdv | 3 (time, lat, lon) | mm/d | Daily mean of intra-platform standard deviation derived from hourly values | |
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quality_flag | 3 (time, lat, lon) | N/A | Mean of PNPR-CLIM quality flags, whose assigned data was used in composite creation | |
num_obs | 4 (time, lat, lon, instrument_id) | N/A | Total number of observations separated by instrument type | |
num_covered_hours | 3 (time, lat, lon) | N/A | Accumulated number of hours, for which data of at least one platform is available on the respective day | |
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platform_name | 2 (time, platform_id) | N/A | Names of all platforms that are used for composite creation for the respective day. The names are allocated to the platform identifier. Platform names are saved as char array. Thus, there is an additional dimension in the netCDF file describing the length of the longest string. | |
instrument_name | 2 (time, instrument_id) | N/A | Assigned names of the specific instrument identifier. Instrument names are saved as char array. Thus, there is an additional dimension in the netCDF file describing the length of the longest string. |
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Variable Name | Dimension(s) | Unit | Description | |
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lat | 1 | °N (degrees north) | Latitude of grid cell centre | |
lat_bnds | 2 | °N (degrees north) | Boundaries of top (northern) and bottom (southern) grid cell edge | |
lon | 1 | °E (degrees east) | Longitude of grid cell centre | |
lon_bnds | 2 | °E (degrees east) | Boundaries of left (western) and right (eastern) grid cell edge | |
time | 1 | Seconds since 1970-01-01 | Time stamp of the current month | |
time_bnds | 2 | Seconds since 1970-01-01 | Boundaries of the time interval covered by time variable | |
platform_id | 1 | N/A | An integer used for internal platform assignment | |
instrument_id | 1 | N/A | An integer used for internal instrument assignment | |
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precip | 3 (time, lat, lon) | mm/d | Monthly mean precipitation that is represented by a single multi-platform composite | |
precip_stdv | 3 (time, lat, lon) | mm/d | Monthly mean of intra-platform standard deviation derived from hourly values | |
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quality_flag | 3 (time, lat, lon) | N/A | Mean of PNPR-CLIM quality flags, whose assigned data was used in composite creation | |
num_obs | 4 (time, lat, lon, instrument_id) | N/A | Total number of observations separated by instrument type | |
num_covered_hours | 3 (time, lat, lon) | N/A | Accumulated number of hours, for which data of at least one platform is available in the respective month | |
Ancillary Variables | ||||
platform_name | 2 (time, platform_id) | N/A | Names of all platforms that are used for composite creation for the respective month. The names are allocated to the platform identifier. Platform names are saved as char array. Thus, there is an additional dimension in the netCDF file describing the length of the longest string. | |
instrument_name | 2 (time, instrument_id) | N/A | Assigned names of the specific instrument identifier. Instrument names are saved as char array. Thus, there is an additional dimension in the netCDF file describing the length of the longest string. |
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Name | Long Name | Type |
CHAN | Channel | 1D |
LAT | Latitude | 2D |
LON | Longitude | 2D |
POS | Scan position | 1D |
PP | Probability of Precipitation | Geo2D |
PR | Precipitation Rate | Geo2D |
QUALITY_PIXEL_BITMASK | FIDUCEO quality pixel bitmask | Geo2D |
SCAN | Scan line | 1D |
UPR | Unmasked Precipitation Rate | Geo2D |
UTIME | Scan time | 1D |
QF | Quality Flag | Geo2D |
BQF | Quality Bit Flag | Geo2D |
A list of global attributes of PNPR-CLIM netCDF output files is reported, as an example, in the following paragraph:
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