Polarized Sub-millimeter Ice cloud Radiometer (PolSIR)

Quick facts

Overview

Summary

Mission Capabilities

Each satellite features a multi-spectral radiometer which uses cross-track scanning to measure over a range of wavelengths between 0.922 and 0.441 mm. With these sub-millimetre wavelengths, the radiometer is capable of penetrating ice clouds and collecting data to analyse partial columns and the scattering of particles within ice clouds.

Performance Specifications

The radiometers have a spatial resolution of 12km. To measure diurnal patterns, the satellites will follow a non-sun-synchronous orbit at an altitude of 475km and a period of 94 minutes. They will be inclined at 52 degrees, allowing coverage of the tropic and sub-tropic latitudes of ±35°. The satellites will orbit out of phase from each other by 3-9 hours.

Space and Hardware Components

PolSIR’s satellite buses will be provided by RTX’s (formerly Raytheon Technologies Corporation) Blue Canyon Technology. The satellite has a design lifespan of 3 years.

Overview

Polarized Sub-millimeter Ice cloud Radiometer (PolSIR) is a cubesat mission under NASA’s Earth Venture Instrument program (EVI). Labelled EVI-6, PolSIR is a mission of opportunity and a member of the Earth System Science Pathfinder program (ESSP). It has been guided by Vanderbilt University’s Dr. Ralf Bennartz, and is designed to study the Ice Water Paths (IWP) of high altitude ice clouds, especially in tropic or sub-tropic latitudes. 1) 8)

 
Ice clouds provide useful insight into our atmosphere’s regulation of radiation as the microphysical properties of the molecules determine whether clouds reflect or absorb solar radiation. Different species of ice crystals form from varying nucleation processes, and as a result have different effective radii and IWP. Furthermore, ice clouds' individual properties are results of radiation at the top of the atmosphere (TOA), connecting radiation at TOA to precipitation and weather systems at the Earth’s surface. Previous studies of such factors have faced errors in their radiation observation around tropic and subtropic regions, with shortwave and longwave radiation being underestimated and overestimated respectively. Hence, PolSIR’s primary objective is to fill this gap and improve estimates of short and longwave radiation emissions. 2) 3)

PolSIR’s secondary objective is to analyse deep convection, an effect of precipitation and movement of air of differing temperatures in a turbulent mixing process. This influences the formation of storms, which in turn have significant agricultural and environmental impacts. PolSIR will collect data on the variability of ice cloud presence in these tropical regions which feature frequent convection flow and thus, vertical motion of air layers. 5)

PolSIR’s two satellites will orbit between ±35° latitude, targeting observations of the tropic and sub-tropic regions. PolSIR employs a radiometer of specific sub-millimeter frequencies (325 and 680 GHz) chosen to observe a gap in previous missions’ analysis. Upper-tropospheric ice clouds can be analysed by creating a series of ice particle columns from deep in the cloud which other frequencies are unable to analyse. As seen in the figure below, PolSIR has the capability to analyse IWP and determine data useful for both convection flow analysis and radiation analysis previously lost in a sensitivity gap.  4) 6)

PolSIR’s instruments come as a result of several other radiometer based missions, such as IceCube. IceCube utilised a radiometer for its ability to penetrate ice clouds and high sensitivity to ice cloud scattering. At a frequency of 883 GHz, IceCube improved on the remote-sensing technology that is now being improved on again with PolSIR. 7)

Iterating upon these learnings, PolSIR’s radiometer uses the frequency of 325GHz for its role in penetrating deep and sensing large snow ice, and 680GHz which is a matured version of the technology used by IceCube (883GHz). 4)

Spacecraft

PolSIR consists of two 12U cubesats each equipped with radiometers capable of 6 channel cross-track scanning. Blue Canyon Technologies is supplying their XB16 spacecraft, which is a 16U class cubesat capable of hosting a 12U payload. The solar array has a power range of 92-108W, with energy being stored from 6.8-20.4Ah. Spacecraft attitude is monitored and controlled by two trackers for a ±0.002 degree uncertainty across all three axes, and an agility of less than 3 degrees per second for immediate attitude changes. 13)

Launch

PolSIR’s twin satellites will orbit at an altitude of 475km, in a non-sun-synchronous orbit at an inclination of 52 degrees. In this configuration, they will jointly achieve a full diurnal sampling of 35°S–35°N latitudes every month. Furthermore, each will have a period of 94 minutes, and will orbit out of phase from each other by 3-9 hours. In their drifting orbit, they will take measurements diurnally to create diurnal patterns of ice cloud phenomena.

The two satellites have a lifetime of 3 years, throughout which they will continuously observe diurnal patterns of IWP, convective flow, and shortwave/longwave fluxes. 6) 4)

Mission Status

• January, 2025: Following review of the design, Director of NASA’s Earth Science Division, Dr. Karen St. Germain, approved PolSIR to move from the Planning Phase into the Implementation Phase. NASA Goddard Space Flight Center is appointed to assemble the PolSIR instruments, under the leadership of Vanderbilt University’s Dr. Ralf Bernnartz, with support from a team of graduate students and researchers in the Earth and Environmental Sciences Division. 11)
• June 12, 2024: Blue Canyon Technologies (RTX) was appointed to manufacture two 12U cubesat buses for PolSIR. 10)
• May, 2023: NASA appoints PolSIR to become an Earth Venture Instrument (EVI); identified as EVI-6, Class D Earth Venture. It was awarded a cost-capped investment of $37-42M, exclusive of launch costs. This comes as a result of recognition from the Intergovernmental Panel on Climate Change (IPCC) regarding the need for improved modelling of ice clouds and atmospheric cloud feedback, especially in diurnal cycles. 9)

Sensor Complement

Polarized Submillimeter Ice-cloud Radiometer

The PolSIR instrument is built to constrain the characterisation of diurnal variability in tropic and sub-tropic ice clouds. The radiometer is being developed by NASA Goddard Space Flight Center.

Featuring cross-track scanning, the dual band polarization radiometers have multiple channels as is seen in the table below. As a passive microwave radiometer, it measures columns and effective radii within ice clouds through penetration of the surface and analyse scattering of particles within the cloud. Each instrument is projected to have a footprint size less than 15km.  12)

A more in-depth analysis of PolSIR’s structure and instruments may be seen in the figure below. 

Ground Segment

PolSIR will downlink data on frequencies between S-Band (2 Mbps) and X-Band (up to and including 10 Mbps) and will receive uplinked information at approximately 100 Kbps. PolSIR spacecraft contain a baseline of 4GB onboard data storage, that can be increased through Blue Canyon Technologies’ high speed data recorder. 13)

References  

1) Loren Data Corp. “Polarized Submillimeter Ice-cloud Radiometer (PolSIR) Mission Principal Investigator (PI) and Science Management contract”  29 November 2023 URL: https://www.fbodaily.com/archive/2023/11-November/29-Nov-2023/FBO-06894169.htm

2) Bastiaan van Diedenhoven, Andrew S. Ackerman, Ann M. Fridlind, Brian Cairns, Jérôme Riedi, "Global Statistics of Ice Microphysical and Optical Properties at Tops of Optically Thick Ice Clouds," Journal of Geophysical Research Atmospheres, 3 March 2020, URL: https://doi.org/10.1029/2019jd031811

3) Gong J, Liu Y, Chen R, et al., "PolSIR Level-2 Algorithm and Data Product Overview," 11th Workshop of International Precipitation Working Group (IPWG-11), July 2024, URL: https://www.eorc.jaxa.jp/IPWG/meetings/tokyo-2024/pdf/Session05/5.5_IPWG_Tuesday_JieGong%20Jie%20Gong.pdf

4) NASA Earth Sciences, “PolSIR,” URL: https://earth.gsfc.nasa.gov/climate/instruments/polsir

5) Vaughan C. “Deep Thoughts on Deep Convection,” State of the Planet. March 2009. URL: https://news.climate.columbia.edu/2009/03/01/deep-thoughts-on-deep-convection/

6) Wu DL, Gong J, Deal WR, et al. “Remote Sensing of Ice Cloud Properties With Millimeter and Submillimeter-Wave Polarimetry,” IEEE Journal of Microwaves, 20 November 2024, URL: https://doi.org/10.1109/jmw.2024.3487758

7) Goddard Space Flight Center, “Atmospheric Instrument Systems and Technology in the Goddard Earth Sciences Division” November 2017, URL: https://earth.gsfc.nasa.gov/sites/default/files/atmospheres/files/GSFC%20Atmospheres%20Instrument%20Report%202017.pdf

8) Hornback J, Jacobs M, Hayes S. “Venture = a Risky or Daring Journey or Undertaking. Is NASA’s Earth Venture Class of Missions Taking a Risky Journey to Create Low-Cost Missions Focused on Innovative Research?” Earth System Science Pathfinder Program (ESSP), 16 April 2024, URL: https://www.nasa.gov/wp-content/uploads/2024/05/01-2024-cs-sym-earth-venture-performance-study-final-r1.pdf?emrc=9706f3

9) Vanderbilt, “Polarized Submillimeter Ice Cloud Radiometer (PolSIR),” 6 February 2024. URL: https://www.vanderbilt.edu/polsir/

10) Raytheon Corporate Communications, “RTX’s Blue Canyon Technologies selected by NASA to provide multiple spacecraft buses for PolSIR mission,” Raytheon News Release Archive, 12 June 2024, URL: https://raytheon.mediaroom.com/2024-06-12-RTXs-Blue-Canyon-Technologies-selected-by-NASA-to-provide-multiple-spacecraft-buses-for-PolSIR-mission

11) Shapiro M, “Vanderbilt University’s Ralf Bennartz to lead NASA mission to study ice clouds. Vanderbilt University,” 14 January 2025, URL: https://news.vanderbilt.edu/2025/01/14/vanderbilt-universitys-ralf-bennartz-to-lead-nasa-mission-to-study-ice-clouds/

12) WMO OSCAR, “Details for Instrument PolSIR radiometer,” 2023, URL: https://space.oscar.wmo.int/instruments/view/polsir_radiometer

13) Blue Canyon Technologies “XB16 SPACECRAFT,” 20 February 2025, URL: https://www.bluecanyontech.com/wp-content/uploads/16U-1_2025.pdf

14) PolSIR, “PolSIR Mission SRR Template,” Living Planet Symposium 2025, 2 July 2025, URL: https://lps25.esa.int/lps25-presentations/presentations/1496/_1496.pdf