Request to trade M7 for M11 at night Christopher D. Elvidge, Ph.D. Earth Observation Group NOAA-NESDIS National Geophysical Data Center Boulder, Colorado USA March 10, 2014

Summary The VIIRS Nightfire product uses multispectral Planck curve fitting to analyze sub- pixel combustion sources, yielding temperature, source size, and radiant heat. Planck curve fitting fails for ~40% of all detections due to insufficient sampling of the Planck curve. There are also false detections from SAA. Proposed Solution: – Collect M11 at night. A detection limit analysis indicates M11 would resolve the vast majority of the current pixels which fail in Planck curve fitting, IF there is a real heat source in the pixel. Noise filtering will be improved by requiring detection in M11 plus M10 or M12/M13. – Drop M7 nighttime collection. M7 is redundant with DNB for Planck curve fitting and provides few detections relative to other spectral bands. Swapping M11 for M7 has a side benefit of reducing downlink data volume. A survey of VIIRS product specialists and data users found no objection to the loss of M7 at night. – Survey sent out to 140 scientists affiliated with the VIIRS SDR and Imagery teams. No nighttime M7 users were identified. No objections to the plan were voiced. – Feedback from Tom Kopp and Ivan Csiszar confirmed M7 is not used in VCM or active fire products at night.

Endorsed by USFS

How did VIIRS come to collect daytime data at night? Original Message Subject: Re: [NOTIFY] Does anyone use M7 nighttime data? Date: Mon, 10 Feb :57: From: Shawn W Miller To: Chris Elvidge Hi Chris, Way back in , I was the one who led the push to have the instrument folks turn these bands on at night, precisely to help with Active Fires (since we were unsuccessful in getting the saturation temperature raised as high as we wanted it in the thermal IR). During that analysis I determined that M11 would saturate for most fires that consumed more than 1% of the area of a pixel - that's the main reason the program doesn't currently have it turned on at night. That's not to say my analysis didn't have errors, or that it still wouldn't provide the value you're looking for, but just a heads-up that you might want to look at the dynamic range of that band if you haven't already. Shawn _________________________________________ Shawn W. Miller, Ph.D. Chief Architect, JPSS CGS Engineering Fellow, Raytheon IIS Office: Cell:

The daytime imaging bands enable robust Planck curve fitting for ~10,000 pixels per night! NGDC’s VIIRS Nightfire was developed under the JPSS Proving Ground Program. Two primary detection algorithms: M10 and M12&M13. Other spectral bands are analyzed in support of M10, M12&M13. Noise is filtered by requiring detection in at least two spectral bands. By modeling the Planck curve it is possible to calculate temperature, radiative heat, and source footprint Radiant heat is key to estimating the quantity of combusted fuel Strong sources have detections in DNB, M7, M8, M10, M12, M13. In this case it is easy to fit a Planck curve.

Three Types of Problem Pixels Would Be Addressed With M11 at Night Type 1: Weak detections with M10 and DNB. Planck curve fitting fails. Type 2: Weak detections with M12 & M13 only. Planck curve fitting are suspect because the of the narrow spectral range of the Planck curve sampling. Type 3: Noise from the South Atlantic Anomaly and aurora.

Type 1: M10 & DNB M10 + DNB detections have white placemarks Approximately 40% of all detections have M10 and DNB detection only. The Planck curve fitting fails. It is not possible to calculate temperature, radiative heat, and source footprint. M11 would resolve most of these cases because an object hot enough to generate an M10 detection will invariably have an M11 detection. North Dakota

Type 2: M12 & M13 only detections The Planck curve fits are suspect due to the fact that M12 and M13 span only a short spectral range. North Dakota

Type 3: False detects occur when SNPP flies through the South Atlantic Anomaly and auroral zones High energy particle detections in the South Atlantic Anomaly can be partially filtered out by the requiring detection in at least one band in addition to M10. Having M11 would improve noise filtering in SAA and auroral zones.

Detection Limit Analysis M11 has lower detection limits than M10 and M13 from 400 to 2000 K. This implies that pixels with weak M10 or M13 detections will also have M11 detection, resolving the where Planck curve fitting.

Would any product or user group be adversely affected by the loss of M7 at night?

M7 Is Not Designed For Nocturnal Imaging Daytime M7 Nighttime M7

Products That Use Daytime M7 VIIRS Cloud Mask (VCM) Active Fire AOT Surface Reflectance Land Surface Albedo Vegetation Indices Snow Cover Ocean Color/Chlorophyll The products in red have “day only” requirements, so they are not produced at night. This is because without sunlight, M7 can not detect clouds, snow and ice, or the land surface. The active fire product uses M7 during the day to calculate a vegetation index.

Inquiries sent to SDR/EDR Teams s asking if any VIIRS product or any processing group makes use of M7 at night were sent to: – 97 member list used by Changyong Cao for the VIIRS SDR team telecons. – 43 member list used by Don Hillger for the VIIRS Imagery team telecons as they were identified as the remaining M7 potential users. I briefed the CCR request on Don's telecon this week and fielded questions. No response came back indicating use of M7 at night from any of the teams.

Pointed inquiries to individuals VIIRS Cloud Mask (VCM) : – Tom Kopp was asked if M7 was used in the nighttime VCM to which the response is: “M7 is not used at night in the VCM. There are no plans to do so either and we can confirm the VCM does not use M7 at night. But to be clear, it [the M7 band] is important to the SDR in daytime granules.” Clouds: – Andrew Heidinger was asked if M7 was used at night for cloud optical properties; no response yet. Active Fires: – Ivan Csiszar was asked in M7 was used at night for the VIIRS operational fire product: “I can confirm that M7 is not used at night (as part of the internal cloud mask tests and to calculate NDVI), but we need to make sure that we define "night" so that the fire algorithm (and any other algorithms that use M7) have the data up to their cut-off value for solar zenith angle.”

Summary of request NGDC requests VIIRS M11 data collections at night in order to extend the ability to estimate temperature, source footprint and radiant heat to smaller and cooler combustion sources. M7 could be turned off to constrain data download volumes and processing requirements. M7 radiances for combustion sources is typically quite low and the bandpass is largely redundant with the DNB. Nighttime M11 data would improve the filtering of false detections associate with the South Atlantic Anomaly and aurora. None of the VIIRS products use M7 at night. No users have been found for M7 at night. M7 is dual gain, M11 is not. Therefore replacing M7 with M11 at night would result in a modest savings in data volume for downlink, processing and delivery. The product is being generated for data from several ground stations to reduce temporal latency. Changes to the HRD channel configuration could affect this product. If M10 was discontinued from nighttime HRD broadcast it could be replaced by I3, which has essentially the same bandpass.

Additional Info Kurtis Thome/NASA to Chris Elvidge (7 Jan/8:29am) Even simple changes in band combinations are affected not only by the specific band predictor pairs but also day/night operation differences, and I-band and M-band pairs. Raytheon does not have any technical issues with modifying band usage, but strongly recommends that any deviation from the current operational approaches be tested on the engineering unit for VIIRS to check that a new band table would operate as desired. This would be true even for J1. Thus, it should be possible to change things, but someone will need to be convinced to have Raytheon do the study. Kurt