{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,24]],"date-time":"2026-03-24T00:57:27Z","timestamp":1774313847728,"version":"3.50.1"},"reference-count":26,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2020,5,8]],"date-time":"2020-05-08T00:00:00Z","timestamp":1588896000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000844","name":"European Space Agency","doi-asserted-by":"publisher","award":["4000124803\/18\/NL\/CT"],"award-info":[{"award-number":["4000124803\/18\/NL\/CT"]}],"id":[{"id":"10.13039\/501100000844","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>FORUM (Far-infrared Outgoing Radiation Understanding and Monitoring) has been approved to be the ninth Earth Explorer mission of the European Space Agency. The mission is scheduled for launch on a Polar satellite in the 2025\u20132026 time frame. The core FORUM instrument is a Fourier Transform Spectrometer measuring, with very high accuracy, the upwelling spectral radiance, from 100 to 1600 cm      \u2212 1      (from 100 to 6.25 microns in wavelength), thus covering the Far-Infrared (FIR), and a Mid-Infrared (MIR) portion of the spectrum emitted by the Earth. FORUM will fly in loose formation with the MetOp-SG-1A satellite, hosting the Infrared Atmospheric Sounding Interferometer \u2013 New Generation (IASI-NG). IASI-NG will measure only the MIR part of the upwelling atmospheric spectrum, from 645 to 2760 cm      \u2212 1      (from 15.5 to 3.62 microns in wavelength), thus, the matching FORUM measurements will supply the missing FIR complement. Together, the two missions will provide, for the first time, a spectrally resolved measurement of the full Earth emitted thermal spectrum. The calibrated spectral radiance will be, on its own, the main product of the FORUM mission, however, the radiances will also be processed up to Level 2, to determine the vertical profile of water vapour, surface spectral emissivity and cloud parameters in the case of cloudy atmospheres. In this paper we assess the performance of the FORUM Level 2 products based on clear-sky simulated retrievals and we study how the FORUM and IASI-NG matching measurements can be fused in a synergistic retrieval scheme, to provide improved Level 2 products. Considering only the measurement noise and the systematic calibration error components, we find the following figures for the synergistic FORUM and IASI-NG retrieval products. In the upper troposphere\/lower stratosphere region, individual water vapour profiles can be retrieved with 1 km vertical sampling and an error ranging from 10% to 15%. In the range from 300 to 600 cm      \u2212 1     , surface spectral emissivity can be retrieved with an absolute error as small as 0.001 in dry Polar atmospheres. Ice cloud parameters such as ice water path and cloud top height can be retrieved with errors smaller than 10% and 1 km, respectively, for ice water path values ranging from 0.2 to 60 g\/m     2    .<\/jats:p>","DOI":"10.3390\/rs12091496","type":"journal-article","created":{"date-parts":[[2020,5,8]],"date-time":"2020-05-08T11:26:00Z","timestamp":1588937160000},"page":"1496","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":20,"title":["FORUM Earth Explorer 9: Characteristics of Level 2 Products and Synergies with IASI-NG"],"prefix":"10.3390","volume":"12","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3492-6472","authenticated-orcid":false,"given":"Marco","family":"Ridolfi","sequence":"first","affiliation":[{"name":"National Institute of Optics, National Research Council, 50019 Firenze, Italy"},{"name":"Department of Physics and Astronomy, University of Bologna, 40126 Bologna, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2689-6629","authenticated-orcid":false,"given":"Samuele","family":"Del Bianco","sequence":"additional","affiliation":[{"name":"Institute for Applied Physics \u201cCarrara\u201d, National Research Council, 50019 Firenze, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Alessio","family":"Di Roma","sequence":"additional","affiliation":[{"name":"Department of Physics and Astronomy, University of Bologna, 40126 Bologna, Italy"},{"name":"Institute of Atmospheric Sciences and Climate, National Research Council, 40129 Bologna, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2218-5790","authenticated-orcid":false,"given":"Elisa","family":"Castelli","sequence":"additional","affiliation":[{"name":"Institute of Atmospheric Sciences and Climate, National Research Council, 40129 Bologna, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2234-6171","authenticated-orcid":false,"given":"Claudio","family":"Belotti","sequence":"additional","affiliation":[{"name":"National Institute of Optics, National Research Council, 50019 Firenze, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Paolo","family":"Dandini","sequence":"additional","affiliation":[{"name":"Laboratory of Atmospheric Optics, University of Lille, 59000 Lille, France"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9149-7926","authenticated-orcid":false,"given":"Gianluca","family":"Di Natale","sequence":"additional","affiliation":[{"name":"National Institute of Optics, National Research Council, 50019 Firenze, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1218-0008","authenticated-orcid":false,"given":"Bianca Maria","family":"Dinelli","sequence":"additional","affiliation":[{"name":"Institute of Atmospheric Sciences and Climate, National Research Council, 40129 Bologna, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Laurent","family":"C.-Labonnote","sequence":"additional","affiliation":[{"name":"Laboratory of Atmospheric Optics, University of Lille, 59000 Lille, France"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4022-8125","authenticated-orcid":false,"given":"Luca","family":"Palchetti","sequence":"additional","affiliation":[{"name":"National Institute of Optics, National Research Council, 50019 Firenze, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2020,5,8]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"151","DOI":"10.1016\/S0022-4073(97)00152-0","article-title":"The impact of far i.r. absorption on clear sky greenhouse forcing: Sensitivity studies at high spectral resolution","volume":"60","author":"Brindley","year":"1998","journal-title":"J. Quant. Spectrosc. Radiat. Transf."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"197","DOI":"10.1175\/1520-0477(1997)078<0197:EAGMEB>2.0.CO;2","article-title":"Earth\u2019s Annual Global Mean Energy Budget","volume":"78","author":"Kiehl","year":"1997","journal-title":"Bull. Am. Meteorol. Soc."},{"key":"ref_3","unstructured":"Collins, W., and Mlynczak, M. (2020, May 04). Prospects for Measurement of Far Infrared Tropospheric Spectra: Implications for Climate Modeling. Available online: https:\/\/ui.adsabs.harvard.edu\/abs\/2001AGUFMGC32A0210C\/abstract."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"4637","DOI":"10.1175\/2009JCLI2874.1","article-title":"Evolution and Trend of the Outgoing Longwave Radiation Spectrum","volume":"22","author":"Huang","year":"2009","journal-title":"J. Clim."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"718","DOI":"10.1002\/qj.596","article-title":"Measurement and simulation of mid-and far-infrared spectra in the presence of cirrus","volume":"136","author":"Cox","year":"2010","journal-title":"Q. J. R. Meteorol. Soc."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"447","DOI":"10.1175\/1520-0442(1998)011<0447:TIOACR>2.0.CO;2","article-title":"The impact of Antarctic cloud radiative properties on a GCM climate simulation","volume":"11","author":"Lubin","year":"1998","journal-title":"J. Clim."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1425","DOI":"10.1002\/qj.132","article-title":"The impact of cirrus microphysical and macrophysical properties on upwelling far infrared spectra","volume":"133","author":"Baran","year":"2007","journal-title":"Q. J. R. Meteorol. Soc."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1239","DOI":"10.1016\/j.jqsrt.2009.02.026","article-title":"A review of the light scattering properties of cirrus","volume":"110","author":"Baran","year":"2009","journal-title":"J. Quant. Spectrosc. Radiat. Transf."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"1505","DOI":"10.1175\/BAMS-D-13-00286.1","article-title":"Far-Infrared radiative properties of water vapor and clouds in Antarctica","volume":"96","author":"Palchetti","year":"2015","journal-title":"Bull. Am. Meteorol. Soc."},{"key":"ref_10","unstructured":"Oetjen, H. (2019). Report for Mission Selection: FORUM, European Space Agency. Technical Report ESA-EOPSM-FORM-RP-3549."},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Harries, J., Carli, B., Rizzi, R., Serio, C., Mlynczak, M., Palchetti, L., Maestri, T., Brindley, H., and Masiello, G. (2008). The Far-infrared Earth. Rev. Geophys., 46.","DOI":"10.1029\/2007RG000233"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"10:1","DOI":"10.1029\/2001GL013909","article-title":"Assessing the climate impact of trends in stratospheric water vapor","volume":"29","author":"Forster","year":"2002","journal-title":"Geophys. Res. Lett."},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Palchetti, L., Brindley, H., Bantges, R., Buehler, S., Camy-Peyret, C., Carli, B., Cortesi, U., Del Bianco, S., Di Natale, G., and Dinelli, B.M. (2020). FORUM: Unique far-infrared satellite observations to better understand how Earth radiates energy to space. Bull. Am. Meteorol. Soc., submitted.","DOI":"10.1175\/BAMS-D-19-0322.1"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"106927","DOI":"10.1016\/j.jqsrt.2020.106927","article-title":"The two-stream \u03b4-Eddington approximation to simulate the far infrared Earth spectrum for the simultaneous atmospheric and cloud retrieval","volume":"246","author":"Palchetti","year":"2020","journal-title":"J. Quant. Spectrosc. Radiat. Transf."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"3541","DOI":"10.1175\/JAS-D-15-0355.1","article-title":"An observationally based global band-by-band surface emissivity dataset for climate and weather simulations","volume":"73","author":"Huang","year":"2016","journal-title":"J. Atmos. Sci."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"3711","DOI":"10.1175\/JCLI-D-17-0125.1","article-title":"Improved representation of surface spectral emissivity in a global climate model and its impact on simulated climate","volume":"31","author":"Huang","year":"2018","journal-title":"J. Clim."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"4367","DOI":"10.5194\/amt-7-4367-2014","article-title":"Towards IASI-New Generation (IASI-NG): Impact of improved spectral resolution and radiometric noise on the retrieval of thermodynamic, chemistry and climate variables","volume":"7","author":"Crevoisier","year":"2014","journal-title":"Atmos. Meas. Tech."},{"key":"ref_18","first-page":"9973","article-title":"MIPAS reference atmospheres and comparisons to V4.61\/V4.62 MIPAS level 2 geophysical data sets","volume":"7","author":"Remedios","year":"2007","journal-title":"Atmos. Chem. Phys. Discuss."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"16297","DOI":"10.1073\/pnas.1413640111","article-title":"Far-infrared surface emissivity and climate","volume":"111","author":"Feldman","year":"2014","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_20","unstructured":"Kokhanovsky, A.A. (2008). LIDORT and VLIDORT: Linearized pseudo-spherical scalar and vector discrete ordinate radiative transfer models for use in remote sensing retrieval problems. Light Scattering Reviews 3: Light Scattering and Reflection, Springer."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.rse.2015.10.037","article-title":"Total column water vapour from along track scanning radiometer series using thermal infrared dual view ocean cloud free measurements: The Advanced Infra-Red WAter Vapour Estimator (AIRWAVE) algorithm","volume":"172","author":"Casadio","year":"2016","journal-title":"Remote Sens. Environ."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"259","DOI":"10.1364\/JOSA.66.000259","article-title":"New Apodizing Functions for Fourier Spectrometry","volume":"66","author":"Norton","year":"1976","journal-title":"J. Opt. Soc. Am."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"419","DOI":"10.1364\/JOSA.67.000419","article-title":"Errata\u2014New Apodizing Functions for Fourier Spectrometry","volume":"67","author":"Norton","year":"1977","journal-title":"J. Opt. Soc. Am."},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Rodgers, C.D. (2000). Inverse Methods for Atmospheric Sounding, World Scientific.","DOI":"10.1142\/9789812813718"},{"key":"ref_25","unstructured":"Del Bianco, S., Carli, B., Gai, M., Laurenza, L.M., and Cortesi, U. (2014). XCO2 retrieved from IASI using KLIMA algorithm. Ann. Geophys., 56."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"233","DOI":"10.1016\/j.jqsrt.2004.05.058","article-title":"Atmospheric radiative transfer modeling: A summary of the AER codes","volume":"91","author":"Clough","year":"2005","journal-title":"J. Quant. Spectrosc. Radiat. Transf."}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/12\/9\/1496\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T09:26:54Z","timestamp":1760174814000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/12\/9\/1496"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,5,8]]},"references-count":26,"journal-issue":{"issue":"9","published-online":{"date-parts":[[2020,5]]}},"alternative-id":["rs12091496"],"URL":"https:\/\/doi.org\/10.3390\/rs12091496","relation":{},"ISSN":["2072-4292"],"issn-type":[{"value":"2072-4292","type":"electronic"}],"subject":[],"published":{"date-parts":[[2020,5,8]]}}}