Low-Earth orbit

JPSS

The Joint Polar Satellite System (JPSS) is NOAA’s low-earth orbitting satellite program. JPSS satellites circle the Earth from pole to pole and cross the equator about 14 times a day in the afternoon orbit to provide full global coverage twice a day. JPSS data is very important for numerical weather forecasting in the U.S. and deliver critical observations during severe weather events like hurricanes and blizzards. JPSS consists of 5 satellites:

  • Suomi NPP

  • NOAA 20

  • NOAA 21

  • JPSS 3 (will be NOAA 22)

  • JPSS 4 (will be NOAA 23)

Each satellite has a VIS/IR imager (VIIRS), an IR sounder (CrIS), a microwave sounder (ATMS), and an ozone mapper (OMPS).

JPSS constellation cartoon

The bubble chart below lists the different products from JPSS instruments. SDRs are Level-1b reprocessed Sensor Data Records. The SDRs are used as input to produce numerous Environmental Data Record (EDRs), which can be considered “Level-2” products. Most users shouldn’t ever have to look at Raw Data Records (RDRs), which are the raw Level-1 data. The figure is courtesy of Amy Huff and Rebekah Esmaili (see https://github.com/jpss-nodd/python-scripts).

Bubble chart with JPSS instrument products

VIIRS

The Visible Infrared Imaging Radiometer Suite, VIIRS, is a scanning radiometer with 5 high-resolution Imagery bands (or I-bands), 16 Moderate resolution bands (M-bands) and a Day/Night band (DNB). The JPSS satellites are in the same orbital plane as NASA’s A-Train constellation but at a higher altitude (JPSS altitude is about 824 km). The JPSS satellites are sun synchronous with an equator crossing time of 1330 (local time).

A rotating mirror reflects radiation onto a set of CCD detectors; a single scan relates to a rotation of the mirror. A single VIIRS scan is completed in 1.779 seconds - the mirror rotation rate is slightly faster than the spec but is within tolerance. The M bands and the day/night band have 16 detectors per scan (750 m spatial resolution per pixel), while the I bands have 32 detectors per scan (375 m resolution per pixel).

VIIRS has a swath of about 3040 km in the cross-track direction, while MODIS has a swath width of 2330 km. With VIIRS, there are no coverage gaps in the Tropics as there are with MODIS.

This table helps summarize the VIIRS channels.

Band Number

Central Wavelength

Nadir Resolution

Gain

I-1

0.640 µm

375 m

single

I-2

0.865 µm

375 m

single

I-3

1.61 µm

375 m

single

I-4

3.74 µm

375 m

single

I-5

11.45 µm

375 m

single

M-1

0.412 µm

750 m

dual

M-2

0.445 µm

750 m

dual

M-3

0.488 µm

750 m

dual

M-4

0.555 µm

750 m

dual

M-5

0.672 µm

750 m

dual

M-6

0.746 µm

750 m

single

M-7

0.865 µm

750 m

dual

M-8

1.24 µm

750 m

single

M-9

1.38 µm

750 m

single

M-10

1.61 µm

750 m

single

M-11

2.25 µm

750 m

single

M-12

3.70 µm

750 m

single

M-13

4.05 µm

750 m

dual

M-14

8.55 µm

750 m

single

M-15

10.76 µm

750 m

single

M-16

12.01 µm

750 m

single

DNB

0.7 µm

500 m

multiple

Geolocation files

Geolocation files are produced separately. Here are their codes:

  • I-band SDR geolocation files

    • GIMGO: projected onto smooth ellipsoid (WGS84 ellipsoid)

    • GITCO: parallax-corrected for terrain

  • M-band SDR geolocation files

    • GMODO: projected onto smooth ellipsoid

    • GMTCO: parallax-corrected for terrain

  • Day/Night Band geolocation file

    • GDNBO: projected onto smooth ellipsoid

  • EDR geolocation files (use ground-track Mercator projection)

    • GIGTO: I-band EDR geolocation

    • GMGTO: M-band EDR geolocation

    • GNCCO: Day/Night Band EDR (NCC) geolocation

See also

Data Viewing

Data Access

Notebooks

Check out the notebook below for an example on how to process and visualize VIIRS data (source notebook).

See also

CrIS

The Cross-track Infrared Sounder, CrIS, is a Fourier Transform Spectrometer that provides high-resolution, three-dimensional temperature, pressure, and moisture profiles. These soundings are used to enhance weather forecasts and to support the monitoring of climate and environmental conditions. CrIS measures infrared radiation emitted by the Earth’s surface and atmosphere.

CrIS works in conjunction with the Advanced Technology Microwave Sounder (ATMS) to provide soundings in both clear and cloudy conditions. It scans in a step-scan fashion, observing a 3x3 array of Fields of View (FOVs) at each step. Each individual FOV has a nadir resolution of approximately 14 km. The full array is called a Field of Regard (FOR) and covers an area of roughly 50 km x 50 km. The instrument has a swath width of about 2200 km, achieving full global coverage in approximately 12 hours.

The CrIS instrument has 2211 spectral channels across three bands:

Band

Spectral Range

Number of Channels

Long-wave IR (LWIR)

650 - 1095 cm^-1 (9.14 - 15.38 µm)

713

Mid-wave IR (MWIR)

1210 - 1750 cm^-1 (5.71 - 8.26 µm)

865

Short-wave IR (SWIR)

2155 - 2550 $cm^{-1}$ (3.92 - 4.64 µm)

633

See also

Data Access

ATMS

The Advanced Technology Microwave Sounder, ATMS, is a cross-track scanning microwave sounder that provides atmospheric temperature and moisture profiles. A key advantage of microwave sounding is its ability to penetrate clouds, providing valuable data in all weather conditions. ATMS data is crucial for numerical weather prediction models and is used in synergy with the infrared observations from CrIS.

ATMS has 22 microwave channels spanning a frequency range from 23 GHz to 183 GHz. These channels are strategically placed to measure different atmospheric properties. The lower-frequency channels provide information on surface temperature and emissivity, while channels around the 50-60 GHz oxygen absorption band provide temperature profiles. Channels around the 183 GHz water vapor absorption line provide moisture profiles.

The spatial resolution of ATMS varies with frequency. Higher-frequency channels have a nadir resolution of 15.8 km, while lower-frequency channels have a resolution of up to 74.8 km. The instrument has a wide swath of approximately 2600 km, ensuring global coverage.

Channel

Frequency (GHz)

Primary Purpose

1

23.8

Water Vapor Burden

2

31.4

Water Vapor Burden

3

50.3

Surface Emissivity, Precipitation

4

51.76

Temperature Sounding (Low Trop)

5

52.8

Temperature Sounding (Low Trop)

6

53.596±0.115

Temperature Sounding (Mid Trop)

7

54.4

Temperature Sounding (Mid Trop)

8

54.94

Temperature Sounding (Upper Trop)

9

55.5

Temperature Sounding (Tropopause)

10

57.29

Temperature Sounding (Strat)

11

57.29±0.217

Temperature Sounding (Strat)

12

57.29±0.322±0.048

Temperature Sounding (Strat)

13

57.29±0.322±0.022

Temperature Sounding (Strat)

14

57.29±0.322±0.010

Temperature Sounding (Strat)

15

57.29±0.322±0.0045

Temperature Sounding (Strat)

16

88.2

Clouds / Snow

17

183.31±7.0

Water Vapor Sounding (Low Trop)

18

183.31±7.0

Water Vapor Sounding (Low Trop)

19

183.31±4.5

Water Vapor Sounding (Mid Trop)

20

183.31±3.0

Water Vapor Sounding (Mid Trop)

21

183.31±1.8

Water Vapor Sounding (Mid Trop)

22

183.31±1.0

Water Vapor Sounding (Mid Trop)

Here are the weighting functions for the 22 ATMS channels.

ATMS weighting functions

See also

Data Access

Data Viewing

NUCAPS

NUCAPS, the NOAA Unique Combined Atmospheric Processing System, is not a sensor itself, but rather a sophisticated retrieval algorithm that produces Environmental Data Records (EDRs). It uses radiances from both the CrIS and ATMS instruments to create high-resolution profiles of temperature, moisture, and important trace gases such as ozone ($O_3$), carbon monoxide ($CO$), and methane ($CH_4$).

The primary advantage of NUCAPS is its ability to combine the high spectral resolution of the CrIS infrared sounder with the cloud-penetrating capability of the ATMS microwave sounder. This allows NUCAPS to generate accurate atmospheric soundings in up to 80% cloud cover, providing a more complete picture of the atmosphere than either instrument could alone. These “all-weather” soundings are critical for weather forecasting, particularly for identifying atmospheric instability that can lead to severe weather.

The NUCAPS product suite provides vertical profiles at the spatial resolution of the CrIS Field of Regard (FOR), which is approximately 50 km at nadir and 135 km at the limb. These soundings are widely used by operational weather forecasters in tools like AWIPS to assess the pre-convective environment.

See also

Data Viewing

Data Access

MetOp

Oribt tracks

The University of Wisconsin – Madison Space Science and Engineering Center provides a resource to see historical and future tracks (next few days) for many polar-orbitting satellites.

Map with orbit tracks for Suomi-NPP.