A compact long-wave infrared (LWIR) channeled spectro-polarimeter (IRCSP) has been developed for integration into the NASA Earth Science Technology Office (ESTO) funded submm-wave and LWIR polarimeters project to measure the microphysical properties of cloud ice. Once deployed, the IRCSP will produce the first linear Stokes measurements ( S0 , S1 , S2 ) of upper-tropospheric cirrus clouds from 8.5 to 12.5 μm. For the first time, a compact, light-weight, and uncooled LWIR polarimeter with off-the-shelf thermal optical components is demonstrated. We report narrowband calibration measurements which quantify metrics of polarimetric system performance. The response of the system to linearly polarized light is shown to agree with both a Mueller matrix model and modulation function for narrowband calibration measurements with an R2 > 0.98 from 8 to 11 μm. The polarimetric efficiency is >0.8 from 8 to 11 μm for narrowband measurements indicating satisfactory performance of the polarization optics. Beyond 11 μm, the agreement is significantly reduced as thermal noise compounds with reduced detector response. Ultimately, the observed system performance is limited by the spectral response of the detector past 11 μm in addition to the thermal noise inherent for the measurements at room temperature.
The trade-off between spectral resolution and instrument throughput is analyzed for a compact, uncooled, longwave infrared (LWIR) channeled spectropolarimeter (IRCSP). The IRCSP was developed as a part of the Sub-mm Wave and InfraRed Polarimeters (SWIRP) project out of NASA's Goddard Spaceflight Center. The IRCSP scientific objective targets measurements of AOLP and DOLP with 1-µm spectral resolution from 8.5 - 12.5µm in a single snapshot. The geometry of the field stop determines the field of view (FOV) of the IRCSP. This work relates the spectral resolution, instrument throughput, and polarimetric accuracy of a spectro-polarimeter to the FOV. The accuracy of linear Stokes retrievals for low temperature thermal targets are predicted for varying FOV and measurement noise conditions. This work presents a method to quantify the achievable accuracy in AOLP and DOLP as a function of field stop dimensions and signal-to-noise ratio (SNR). While smaller field stops are shown to improve accuracy as the spectral resolution is increased, low SNR is the dominant source of error for the IRCSP prototype. For the IRCSP, a SNR of at least 80 is required to produce DOLP measurements with < 5% error for targets with DOLP < 0.2.
A compact long wave infrared (LWIR) channeled spectro-polarimeter (IRCSP) has been developed for integration
into the ESTO-funded Submm-Wave and LWIR Polarimeters (SWIRP) project to measure the microphysical
properties of cloud ice. The IRCSP rotates incident linearly polarized light using the combination of a quarter
waveplate with a fast axis at 45◦ and a thick birefringent crystal; the output polarization state’s orientation is
then a function of wavelength. To modulate and then measure the rotated light, a subsequent wiregrid linear
polarizer tilted at 20◦ generates two output paths with opposite polarities in reflection and transmission to enable
joint radiometric and polarimetric measurement and correct for atmospheric attenuation. The two symmetric
optical paths following the linear polarizer each consist of a diffraction grating and uncooled microbolometer to
simultaneously measure the resulting intensity fringes. Angle and degree of linear polarization (AOLP, DOLP) are
retrieved across 8.5-12.5 µm with 1 µm resolution using Fourier decomposition of the modulated spectrum. The IRCSP will not only measure H-V variance but will produce the first full linear Stokes measurements
(I, Q, and U) of upper-tropospheric cirrus clouds in the LWIR. Following thermal and polarimetric calibration,
the polarimeter is expected to achieve 0.5% DOLP accuracy over 90% of the spectral band.
Cloud ice play important roles in Earth’s climate and weather systems through their interactions with atmospheric radiation, dynamics, energy and precipitation processes. Submillimeter (submm) wave remote sensing at 200-1000 GHz is able to provide the sensitivity not covered by visible (VIS)/infrared (IR) and low-frequency microwave (MW) sensors (10-183 GHz), and measure cloud ice in the middle-to-upper troposphere. The IceCube 883-GHz cloud radiometer is the latest of NASA’s efforts to advance the technology readiness level (TRL) of submm-wave receiver technology for future compact, low-cost implementation of Earth observing systems. Emerging CubeSat opportunities allow a fast-track development and spaceflight demonstration of IceCube on a 3-U CubeSat. Funded by NASA’s In-Space Validation of Earth Science Technologies (InVEST) program and Science Mission Directorate (SMD), IceCube is the first CubeSat developed and flown by Goddard Space Flight Center (GSFC) in 2.5 years, using commercial off-the-shelf (COTS) components and subsystems. It was successfully released from International Space Station (ISS) in May 2017, acquired 15-month science data and produced the first global map of the 883-GHz cloud ice. It achieved all mission objectives and provided a pathway for future cost-effective cloud observations from CubeSat constellation.
The Johns Hopkins University Applied Physics Laboratory (JHU/APL) is developing a compact, light-weight, and lowpower midwave-infrared (MWIR) imager called the Compact Midwave Imaging Sensor (CMIS), under the support of the NASA Earth Science Technology Office Instrument Incubator Program. The goal of this CMIS instrument development and demonstration project is to increase the technical readiness of CMIS, a multi-spectral sensor capable of retrieving 3D winds and cloud heights 24/7, for a space mission. The CMIS instrument employs an advanced MWIR detector that requires less cooling than traditional technologies and thus permits a compact, low-power design, which enables accommodation on small spacecraft such as CubeSats. CMIS provides the critical midwave component of a multi-spectral sensor suite that includes a high-resolution Day-Night Band and a longwave infrared (LWIR) imager to provide global cloud characterization and theater weather imagery. In this presentation, an overview of the CMIS project, including the high-level sensor design, the concept of operations, and measurement capability will be presented. System performance for a variety of different scenes generated by a cloud resolving model (CRM) will also be discussed.
A miniaturized long-wave InfraRed (LWIR) spectro-polarimeter is being developed as a prototype for the Compact Submm-Wave and LWIR Polarimeters (SWIRP) project. The polarimeter in development is a compact (20x20x40 cm) conical-scan instrument to measure the polarimetric radiation from ice cloud scattering at mm- submm (220 and 680 GHz) and IR (8.6, 11, and 12 m) bands. The LWIR polarimeter will provide a series of polarization measurements across the 8.5 - 12.5 micron band, measuring the full set of linear Stokes parameters (I, Q, U) as a function of wavelength. The spectro-polarimeter uses a combination of birefringent crystals, a Wollaston prism, a diffraction grating, and an uncooled microbolometer array to measure both the degree and angle of linear polarization across the spectral bandwidth by modulating the polarization flux in wavelength with a high order retarder.
The Johns Hopkins University Applied Physics Laboratory (JHU/APL) has created a unique design for a compact, lightweight, and low-power instrument called the Compact Midwave Imaging Sensor (CMIS). Funded by the NASA ESTO Instrument Incubator Program (IIP), the goal of this CMIS development project is to increase the technical readiness of CMIS for retrieval of cloud heights and atmospheric motion vectors using stereo-photometric methods. The low-cost, low size, weight and power (SWaP) CMIS solution will include high operating temperature (HOT) MWIR detectors and a very low power cooler to enable spaceflight in a 6U CubeSat. This paper will provide an overview of the CMIS project to include the high-level sensor design.
Obtaining temperature, pressure, and composition profiles along with wind velocities in the Earth’s
thermosphere/ionosphere system is a key NASA goal for understanding our planet. We report on the status of a
technology development effort to build an all-solid-state heterodyne receiver at 2.06 THz that will allow the
measurement of the 2.06 THz [OI] line for altitudes greater than 100 km. The receiver front end features low-parasitic
Schottky diode mixer chips that are driven by a local oscillator (LO) source using Schottky diode based multipliers. The
multiplier chain consists of a 38 GHz oscillator followed by a set of three cascaded triplers at 114 GHz, 343 GHz and
Ice clouds play an important role in the energy budget of the atmosphere as well as in the hydrological cycle.
Currently cloud ice is one of the largest remaining uncertainties in climate models. Large discrepancies arise
from different assumptions on ice cloud properties, in particular on microphysics, which are not sufficiently
constrained by measurements. Passive sub-millimeter wave (SMM) techniques have the potential of providing
direct information on ice content and particle sizes with daily global coverage. Here we introduce a concept for a
compact 2-receiver SMM sensor and demonstrate its capabilities on measurements of ice content, mean particle
size, and cloud altitude.
Passive radiometers at 100-700 GHz offer great potential for remote sensing of cirrus clouds and upper-tropospheric water vapor from space because radiation at these frequencies can penetrate and interact with cirrus clouds without being cut off at/near cloud surface. This paper focuses mostly on satellite microwave observations from UARS MLS at 186.5 and 203.2 GHz. Advantages of limb-viewing geometry include better vertical resolution and less contamination of Earth's surface conditions since the limb background radiance depends only on pointing and water vapor abundance. MLS radiance measurements show that water vapor and cloud signals are separable with frequencies of different sensitivities to water vapor. The cloud-induced radiances can be used to directly retrieve ice water content at 14- 18km altitudes if the ice particles are smaller than 100 microns. Model simulations at these frequencies are also presented for various cloud types and heights. With the modified MLS radiative transfer mode, we are able to simulate limb and nadir radiances at all frequencies between 10 and 1000GHz for both cloudy and clear atmospheres. Our sensitivity studies show that brightness temperature depression at the lowest MLS tangent height can be used to infer cloud height and ice content in the upper troposphere. With more channels near 122, 240, and 640 GHz, we find that the chance of separating cirrus cloud and water vapor is greatly enhanced, and these radiometers are to be flown as the future MLS on board NASA CHEM-1 spacecraft.